Battery Technology – Tales On Two Wheels

Ebike Battery Charge Safety: Use A Cutoff Timer

Lets easily add a layer of extra protection to help safeguard your home and loved ones from a battery fire.

We’ve all seen the news reports. When compared to the number of ebikes out in the world, battery fires are extremely (EXTREMELY) rare. But when they do occur they can be catastrophic to life and property.

As a daily commuter who also uses an ebike for an auto replacement, I have been charging daily for years. In fact, since I charge at home and at work, I am generally charging twice daily. So I do a lot of charging, which increases the possibility of a failure, even if it is a small one.

Lets skip to the good part first:
Here is the light-duty timer I use. It costs a whole US$9.99 on Amazon. I have several scattered around at my home, my office and in a couple of garages.

With that out of the way, I’ll spend the rest of my time telling you how to go about using it.

What Kind Of Failure?

I have had chargers fail to stop at the target voltage on three separate occasions: They kept on charging. In one case I was using a premium charger with an 80%-charge setting, that was supposed to stop at 55.4v on my 14S/52v pack. A 52v pack is really fully charged at 58.8v. I walked into my garage and saw the charger with its fan merrily humming along; its little red light telling me it was feeding current into my battery… and it was now at 59.5v. Luckily for me it wasn’t enough to cause the battery to combust, which it could have if I hadn’t walked in and reacted appropriately

The second time it happened was almost exactly the same story. Diagnosis worked through with the charger manufacturer determined an internal component failure. They were prompt with warranty replacements, but who is going to warranty my garage?

What About The BMS?

All drama aside, the BMS likely stopped the battery from accepting the current from the charger at 59.5v. This second layer of safety prevented disaster.

Whats a BMS? There is a layer of protection inside the battery. Ebike batteries typically have a Battery Management System inside that is supposed to stop accepting current if an overcharge is in progress. But if you read the headlines, you already know those can fail too.

As part of my solution to this problem, I started using chargers made for outdoor commercial and municipal use. These units have Mean Time Between Failure ratings in the hundreds of thousands of hours. They are built to work trouble-free for decades.

That is a whole different story explored here: An Ultra-Reliable Ebike Battery Charger.

Add Another Layer To The Onion

We’re going to address the failure-to-stop risk specifically: Plug a countdown timer into the wall, plug the battery charger into it, and set the timer to physically cut the AC power clean off before the battery even has the chance to reach a 100% state of charge, let alone an overcharge. If everything works correctly, this adds significant safety to routine charging.

Whats a Countdown Timer?

Think of a kitchen timer. You want something to cook for 10 minutes, so you set your timer to ’10’ and when 10 minutes expires, you hear the timer going off with a bell. If you have an oven with a cooking timer, it will also shut the oven off.

So What?

Thats what we’ve got here: An oven timer that plugs into the wall, and instead of going ‘Ding’, cuts the power from the wall socket to the charger when time runs out.

What that will do is stop a charger from even enjoying the possibility of failing and overcharging your battery. So we will be gaining two things: First, we’ll be making it more difficult for the charge process to induce a battery to combust. Second, we will be creating a way to charge the battery to a less-than-100% level, which will lengthen its lifespan.

Extending Battery Life

This second benefit is optional, but makes sense to take advantage of if you can. If this is a new topic for you, here is a good explanation of the plusses and minuses of the practice. I have cue’d it up a couple minutes in to skip the technical portion of the explanation.

How Do We Set The Timer?

You may have to go on a short fact-finding mission. You need to know how much voltage your charger puts into your battery in a given time period. You need to either have a charger that displays the current voltage level, or an ebike display on your handlebars that shows current battery voltage (i.e. the display shows something like “46.2” volts instead of showing five bars in a pictograph, which is functionally almost useless, but not uncommon). If you don’t have a voltage display, you will want to fudge one.

Two DIY ways to do this

Use a Multimeter/Voltmeter and take a reading off of your battery leads
Use A Watt/Voltage Meter and plug it inline to your charge plug or cord

I describe the Watt/Voltage Meter in a fair bit of detail in the ultra-reliable ebike battery charger article, so I will, for now, just link you to it and let you take it from there. You can use that information, along with the separate instructions on how to make dependable crimp connections, to put together an inline meter fairly simply. Additionally, you may be able to come across a meter that just plugs straight into your battery.

When we get into the description of doing a robust DIY timer, one of the optional ways to do it will let you directly attach an inline meter.

We’ll discuss an inline meter as seen above, when we describe a custom timer build in a separate article.

You could also use a multimeter, or voltmeter. Those are pretty simple devices you can get for cheap online, or in your local hardware store. You don’t have to spend a lot of money to get one much more accurate than the typically marginal accuracy of ebike displays and watt meters.

Here is a cheap multimeter (US$9.99 at time of publication) that will do the job. I am linking it here chiefly because it has an instruction manual written in understandable English.

For about US$35, you can get hold of a much higher quality product. This unit has a neat feature where the leads you need to plug into for a given job are lit up with little LED guide lights so you can’t screw that part up.

Since I do a fair bit of hobby work around electrical things, I use this slightly fancier model, that runs about US$60. Its a little more accurate, and has a couple of added bells and whistles. Using it I found my voltage display on my Bullitt hill climber was consistently 0.5v lower than the actual battery voltage.

Find Volts-Added-Per-Hour

Now that we have a method of determining battery voltage, lets figure out how much our charger adds in an hour.

I plugged my multimeter’s leads into my battery charge plug. I get a reading of 55.8v. Thats my starting point. I plug in the charger and set an alarm to come back in one hour. My alarm goes off and I hustle back to the bike to take another voltage reading.

57.2-55.8 = 1.4. My charger puts in an additional 1.4 volts into the battery per hour. It is not such a bad idea to run the battery back down and test it again. Go for a third time on general principles. See if you come up with the same number or maybe you want to average three slightly different numbers.

A Worthwhile Detail To Note:
Ebike battery chargers use a method commonly referred to as “smart charging”. Technically speaking, this is what is known as “CC+CV Modes”, where the Constant Current mode pumps power into the battery at the charger’s full current level (usually something like 2 amps). But when the charge starts approaching the voltage limit the charger is set to reach, it switches to Constant Voltage, which slowly ramps down the current being fed into a battery until it gently stops at the final target voltage.

So, bearing in mind the above, we don’t want to be measuring the rate of volts-added-per-hour when we are up near the top of the battery’s capacity, because we will be measuring when the charger is in a ‘slowing-down’ mode.

Now What?

Well, in the above example, if my battery is at 55.8v, and I want to charge it to 100%, I now have an idea how long it should take to fill it up. My 52v battery is fully charged at 58.8v. So 58.8-55.8 = 3. I need three volts. My charger charges at 1.4v per hour … and I know CV mode will slow the charge rate down near the top.

I could be conservative and just set it for two hours, knowing 2.8v is close enough to 3v, and its safer to come up to a bit less than 100%. Or if I need that 100%, I can set it to 3 hours. That is too much time, but not by much thanks to the CV mode slowdown at the end.

In practice, this is a lot more thought than you will need to put into the process on a routine basis. What you’ll be doing is ballparking what you set the timer to, and even if you go over or under by a bit, if you do your part on the math it will not be enough variance to matter if Something Bad happens.

And if you use the timing method to cut power off at a lesser charge state of, say, 80%… you can routinely be off a bit and instead of risking a problem, you’ll end up with maybe an 83% charge. Or 78%. Not enough to matter on most rides.

Myself personally this is exactly how I ballpark my charges with my timer: I don’t worry about getting anything exact and I shoot for 80%-ish.

We Are Ready To Use A Timer

So we’ve done all of our homework. Its time to plug in a timer. What timer should we use? I personally prefer mechanical timers. The old-school spring-wound kind that are immune to weirdness like power interruptions. The kind that are not programmable and are thus not subject to programming mistakes. The kind that need a positive action to set, and are not so susceptible to a little oops like pushing the 4 hour button instead of the 2-hour button. Also a mechanical timer is more granular in how you set it. If you want an extra 10 minutes on today’s charge you just turn the dial another click or two.

Here’s the timer I have been using. Amazon tells me I have bought five of them over several years.

Picture taken at my professional photo studio (i.e. on my garage floor)

Its a whopping US$9.99 at the time I am writing this. I have been using them for years and they work easily and effectively. Is this a robust solution? No it isn’t. Its just a super cheap little timer. Folks on the internet have taken theirs apart and reported the mechanism inside is not very sturdy. In recent weeks I have found my main one at my home is feeling a little worn out when I turn the dial.

BUT its one hell of a lot better than nothing. And if its this or nothing, spend the ten bucks, get this and hopefully you will be a little safer for having it.

If instead you want to try and do this job with something a little better made, then read Part 2 (coming later in September 2023), where I

Build a Heavy Duty Countdown Timer

Range Anxiety? Be Prepared (and Stop Worrying)

Want to take a long trip with an ebike? Just want to proof yourself against running out of juice on your commute? Here are a variety of solutions.

I’ve put rather a lot of effort into proofing myself against running out of battery juice. In all the years I have been using an ebike as a daily driver – almost always for utility rather than for recreation – I have never run out of battery power. Even when I’ve forgotten to charge before a ride (more on that below).

There Are Solutions

Lets explore some range-extension options. Hopefully you’ll come across something here you hadn’t thought of and can take advantage of.

Use a Big Battery

This is the most obvious one. If you don’t want to run out of gas, put in a big gas tank. This is not a new idea. Nowadays when a gearhead hears about a Corvette Z06, a super fast, light and powerful version of that car comes to mind… but back in 1963, if your option code was RPO Z06, that meant you had the “big tank” Corvette… with a freaking 36 gallon gas tank to minimize refueling stops during races. Or Cannonball runs.

So not a new idea.

If you are doing a DIY ebike conversion, unless you have specific weight goals, you typically want to fit the biggest battery you can afford. Same goes for a manufactured ebike. If it has a larger battery option… you want that. Whether you can take advantage of an option will boil down to the size of your wallet. An XL-sized battery will also let you preserve your battery by charging it to 80% or 90%, but thanks to it being oversized you still have enough in the tank to go wherever you please.

I am all about big batteries on the bikes I build. The Great Pumpkin has a 31 amp-hour, 52 volt custom triangle pack. The Lizzard King has a 32ah/52v brick hiding under its floor. That ties for biggest pack in the fleet with 2Fat – now a recreational bike, it needs big power to run through remote stretches of beach without inland access. That bike has two parallel’d 16ah/52v packs joined together to make a single 32ah battery.

Bigger is better only up to a point. Big batteries equal big weight. So there’s a limit to what you can and should get away with. You can’t go this big on normal neighborhood ebikes, nor should you.

With all that said, going big on a battery can also save your bacon when you do something like forget to charge your battery… there’s enough extra capacity to eke out a ride home rather than having to figure out a way to sleep over at the office.

Bring Along a Spare Battery

This is my least favorite solution, but it may work for you. If you have a battery, buy another one just like it and toss it into a backpack or pannier. Swap it in when needed. This is probably most likely going to appeal to folks with a manufactured ebike and thus no other options. Unfortunately with a solution like this, you can’t get anywhere near as much out of two batteries as you would be able to for a big single one, or for two joined together in parallel (you can to only partially drain each of your packs, hence the loss in capacity). But you suffer the same weight penalty.

Sidebar:
Don’t parallel batteries together unless you know EXACTLY what you are doing. Running packs in parallel increases the potential for danger dramatically, and should only be messed with by folks with the experience to know how to mitigate those increased risks.

Onboard Charging (Permanent Mount)

I have written up my experiences with using Mean Well power supplies as CC+CV ‘smart chargers’, and mentioned they are fanless and weatherproof. This and the fact they have mounting tabs means they can be mounted permanently. Assuming the bike is large enough to have a brick bolted on without anyone really noticing. That can mean cargo bikes and any bike with a front rack – the charger works great as a rack deck. And on the front, you don’t really miss the fact you can’t put a rack trunk on.

Pictured above on the left: The Big Fat Dummy and its 185w/3a charger gassing up at the park. The charger is bolted onto the lower deck, up front on the rack. On the right: The Great Pumpkin‘s 320w charger on the front rack is good for 5 amps.

The 480w monster now on the front rack of 2Fat is good for a whopping 8 amps. Its supersized, as when I need a recharge on that bike I am in the middle of nowhere and facing darkness, fog … and may need to negotiate with an unpleasantly high tide if I dawdle.

Onboard Charging (Carried in a Bag)

You don’t always want to be lugging a charger around; nor do you always have a place to bolt one on. I have both 185w and 320w portables that I bring along occasionally on bikes that don’t have a permanent charger mount. For instance, I didn’t want to add a heat-generating charger to the largely enclosed basement battery box on The Lizzard King. So I carry the 320w unit you see below when circumstances warrant (not the shoe. Thats just there for size comparison). Being able to pump in 5a into any battery is going to add a whole lot of range if you plug in while having lunch.

Speaking of open outlets, where are they best found? Here in the USA I have really good luck with public parks. Oftentimes a picnic canopy will have a working power outlet. You can also stop at a roadside cafe, shop or gas station and ask the owner if you can plug in while you are there visiting. This works best if you are stopping somewhere for lunch and will be there for awhile. I’ve also found plugs attached to the outside of restroom buildings at state parks.

Obviously, this approach works best on regular routes where you can determine in advance what is available. Keep your eyes open, scope out your options and file that information away for the time when you need to use it.

I include a ‘Y’ plug in my kit so if I am asking someone to plug into their AC power, I am proposing to share it, not take it over.

Don’t Be Such a Pig

This next one is obvious… or is it? Its a technique I have used and it gets the job done so here goes:

Use less power, as in dial back the assist. My Bullitt with its Great Big Battery was about 3 miles into a 16 mile Saturday morning Costco run when I realized I had forgotten to charge it after work on Friday. Its 52v/14S battery reads 58v when its full, and was already down to 52v when I realized my mistake. Not only would I be blowing my morning turning around and going back home, it would be hours before that battery was charged. I decided to just go for it. So I reduced my assist to the minimum and continued. When I returned home with a cartful of groceries stuffed into my cargo box and panniers, I was down into the mid 40’s, voltage-wise – and more than a little worn out.

But I made it. I wouldn’t have if I had not gone overboard with the size of the battery.

After this I made sure I carried a charger with me on these trips. There is a park midway on the journey with a publicly available power plug. I can plug in, sack out and catch a nap next to a water fountain and be on my way. Late… but I’ll have beaten the system.

Charge at Public (J1772) EV Charging Stations

Yes really. It may be difficult to find an open plain vanilla AC power outlet that you can use… but nowadays electric vehicle (as in automobile) charging stations are popping up all over the place.

If you do not live in the USA, you will want to find a different adapter than what I am describing below (from what I hear non-USA charging stations in the EU are much more likely to have an ordinary, separate outlet available for public use).

But in the Land of the Free, this may be the only obviously available power plug you can get hold of. I’m seeing them increasingly in parks and ordinary store parking lots. Likely they are also springing up at the more refined campsites and national parks.

This is my J1772–> Nema 5-20 adapter for plugging into an EV charger

This is an option that hasn’t been available until recently, and is still not widely known or even understood. Above is a picture of the adapter I have. It plugs into a USA-standard J1772 EV charger plug and terminates in a female NEMA 5-20 plug on the other side. NEMA 5-20 plugs are also compatible with NEMA 5-15 plugs. Folks in the USA know of the 5-15 as your garden variety 3-prong grounded electrical plug. Using this adapter, you now have a bridge directly from a 240v EV car charger to a plug that you can connect your charger into.

Fzzzzzzzz… BOOM!

Thats what could happen if you just plug in without making sure your charger can handle 240 volts of current versus the usual 120.

Here’s the thing: Many ebike chargers are manufactured to run on global power grid voltage. In the USA, we use 120v. Much of the rest of the world uses a lot more volts. 240v in particular. So if you are manufacturing chargers and want to sell them everywhere, you make one that can handle the various voltages right out of the box, so you only have to make one model. However, you can’t count on this feature being there. So check first.

How can you tell? Look at the fine print on the label. The really tiny print that you never read. In the case of the Mean Wells I use, its written clearly in big letters, since they are meant for commercial use and nobody cares if they look pretty.

Yup it’ll handle 240 volts, alright. Since I have also made chargers for relatives who use them on their ebikes in the EU, I know they work just fine on the higher EU voltages.

But thats me. YOU have to figure this out for yourself on your own charger. You won’t know until you go look.

So Much For The Good News…

Here comes the bad news: These adapters are expensive. I have seen them selling for as much as $200. Oddly enough, after some googling I found a seller only an hour or so down the road from me who seems to have the lowest sale price on the web. I paid $85 for mine. Thats still a lot. Lets hope the price is only going down as these types of units become more common.

Or better yet, lets hope that EV charging stations in the USA start commonly having normal AC plugs available.

Whether that happens or not, you should be able to do one or more of the things above, and turn range anxiety into something you used to have … but don’t anymore.

A Backpack Ebike Battery… Are You Insane?!?

If all I did was write internet posts, I’d still hate this idea. But circumstances made me try one. I knew almost immediately how wrong I had been.

Brace yourself, because, if you haven’t already tried it, and you are like most people, you probably think this is the worst idea, ever. I was one of those people. Then I built a bike that simply had to use a backpack battery as its power source. I held my nose, gritted my teeth and just did it. I dreaded the result right up until I rode it for the first time.

Look at the two pics below. Where’s the battery? Nowhere. Nowhere in the picture, at least. I was wearing it. In the image at right, I have used subtle visual cues to highlight the silicone-insulated XT90 connector I plug into.

By the way, that is a Cyc X1 Pro Gen 1 motor. The little bag houses a BAC800 controller that reached 60 amps of continuous output before I chickened out and lifted.

What problem are we solving?

A backpack battery should obviously not be your first choice, so why do one at all? When doing a DIY ebike build, there are some donors that just don’t have space for a battery.

Where the hell am I going to fit a battery on this bike? I will deliberately NOT answer that question here.

Fresh out of the box from Guerilla Gravity: My Smash 29er; one of their very last alloy frames before they switched to carbon fiber. The tires aren’t even dirty. Lets take a picture cuz it will never be this clean again.

In an earlier draft of this post, I wrote up all the different things I thought of or actually tried, and abandoned because they sucked for one reason or another.

But that is going off into the weeds as this discussion is about backpack batteries, not build or donor choices. So lets table all that talk and just stipulate: We have this bike that we have to work with. we looked at alternatives (remember… I hated this idea at the time), we are left with one choice:

The battery has to be in a backpack

Once I accepted the fact I was stuck doing a backpack, all that was left were materials and ergonomic/mechanical choices. i.e. just make it and do it right.

Pack Choice

If you listen to the experts on the internet (thats a joke in case you missed it), whenever the subject comes up you hear all about how a battery on the back of a rider is a bomb just waiting to go off. There is some truth to this. Flying off the bike and landing on your back on sharp rocks is a really bad thing made a whole lot worse if a li-ion battery is your crash bumper.

There’s also a lot of talk about how the world will end if you put your battery weight up on your back, but we’ll get to that one later.

The solution for safety is to use a hardshell pack of some sort, of the kind you see used on sport motorcycles. I picked a 20L Boblbee GTX from Point65.

Nope, it sure as hell isn’t cheap (I paid about $200 for mine which is way less than they are now), but remember that unexploded bomb thing? Its for real and a hardshell pack solves that problem. It also provides you with spinal protection in case of a crash. And you also get something that addresses another negative the villagers are shouting about: A pack like this form fits your spine, hugs your body and never shifts – not even a little.

I suppose if you had to, you could use a soft pack and then stick your battery into a 30 cal or 50 cal ammo can. Drill a hole in a corner for the power cable exit and it would work, but that can is going to be a lot of weight to carry. Still, if you want a cheap, safe solution that uses a conventional pack… thats it. I’m sure you will figure something out on the shifting thing. I know I have packs that don’t shift. Much.

Really though… this is a problem you need to throw money at to properly solve. In my case I spent about half of retail by finding a vendor closing out an old model and blowing them out at a big discount.

Battery placement inside the pack

You do not want the battery bouncing around freely inside that hardshell pack. Each battery and backpack combo is different, but the core of the solution is to stabilize it with dense, closed-cell padding. I didn’t say wrap it tightly in foam so it overheats (put down that pitchfork). However, part of a smart DIY plan is to use cells that can take a murderous flogging without heating up in the first place. I used the old standby Samsung 25R cell for mine.

For my pack, I add in a little judicious padding. Then sprinkle some tool bags in there (so no little bags on the bike). Job done. Its not moving around.

The Smash, post build but before the first **real** ride (its too clean). All those bags violated my Anti-Festooning Rule and went into the backpack, although the top tube bag only contained soft towels meant for nutcracker protection. Maybe I should have left that one.

Figure out the wiring / connection

This is the tricky part because if you get this wrong and stay aware of the cable, you will hate your ride. First off, I used a short 8ga XT90S extension directly off the main battery output. I pretty much do this on every battery connection on any bike so, when connecting and disconnecting the pack, I’m visiting the wear and tear on a cheap replacement connector and not a live cable soldered into the pack. I also use a pair of XT60 pigtails to make a similar extension cable for the charge connector. Same idea. I’ve had my bacon saved doing this and the experience of just being able to throw away and replace a cheapie extension made this a go-to for me on everything.

The short XT90S extensions are at right. You think thats a lot of pigtails? Doesn’t take much to run out of spare parts… especially these days.

Next comes a long length of true 10ga power cord, made into a long XT90S extension cord. This is what will go from the battery to the motor and its several feet long. How long exactly? I measured out enough to exit the pack, run down my back, down thru my legs and still be long enough to never tug if I am standing on the pedals and bouncing around at the same time.

OK… great… what if I’m sitting down? A cable long enough to stand up with is going to be all kinds of awkward when doing what you do most: Sitting. I spent a fair amount of time trying to figure out what to do about this. A lot of others have done some sort of elastic bungie contraption. I tried that and felt it needed too much strain to extend, and carried a risk of pulling apart the connection at the motor. I needed something that reliably retracted my cable and extended it without much resistance.

And here’s the solution: The Key-Bak Super48 HD. This is literally the direct descendant of that chromed steel extendo keyring thing that every janitor in the United States has on his belt. Except they aren’t chromed steel anymore.

They’re kevlar.

The model I bought has a 48″ extension length, with their lightest 8 oz pull and a kevlar cable. Its so lightweight, it doesn’t impart the same feel of indestructability that the old steel pucks had, but I have been using it since mid-2019 and so far it shows no sign of wear. You can see from the Amazon link above that there are other models of varying lengths and pull weights. You can even get one with a steel cable. Since I’ve been using mine, I can say its 48″ extension is plenty, and the light 8 oz pull makes its operation completely unnoticeable.

How do you make the Key-Bak work?

What you need is a ball attached to your power cable. The cable threads through the key ring and stops at the point where the ball – which is bigger than the ring – is reached. You place the ball at a point down your back and to the side, so there’s more than enough cable slack to let you stand on the pedals, but not so much it gets in your way.

When you stand up the keyring lets the cable extend until the ball stops it. When you sit back down, it retracts back up behind you. Simple and effective. You never have excess cable down around your legs getting in the way. If you need more, the light 8 oz pull lets it happen without your even noticing its there. In fact, you really don’t know its there at all because its placed where you can’t see it, behind you and to the side. Out of sight and out of mind.

Once I spent some time figuring out the cable length needed to do the job right, and where the ball needed to be, I built and positioned the ball as follows:

A strip of leftover silicone handlebar grip roughly 1.5 inches long. Since I have used Wolf Tooth Fat Paw grips and ESI Extra Chunky XXL grips with my Jones bars on various bikes over the years, I have leftovers from grips that were cut off.
Plenty of silicone X-Treme sealing tape.
The silicone grip segment – since it was already sliced off a set of handlebars – already had a slit in it to let it slip over the cord. Wrapping silicone in silicone tape sticks instantly, and doing so – with overwrap onto the adjacent power cord, tightly affixes it so its not moving, ever.
Silicone tape fuses permanently to itself and isn’t going to unravel.

The above is just one way to do this. In my case with spare stuff laying around in my garage.

Here’s the whole setup, laid out so the cabling is visible (right side). Note the key ring and the little foam dingle-ball that makes the whole idea work. Click to zoom in.

A close-up of the keyring retainer in position. Note the inert (siliconed) XT90 cap over the otherwise open, disconnected battery-to-motor connection.

Whats With The Cargo Net?

With a 20ah battery, two small tool bags (one on each side of the pack) and an electric pump, the interior of the backpack is pretty much full. I found some hooks that work well with this pack on Amazon, and applied them to the pack and the net. Now I have the ability to stuff something onto the exterior of the pack. Usually that is my veteran Condor Summit Zero and maybe a small, flat pouch for wallet and phone if I can’t stuff them into the handlebar bag.

Funky hooks. Kind of a specialty choice that work just for this particular pack’s oddball equipment slots.

What is it like when you ride it?

I wasn’t expecting a good experience. The idea of being tethered to the bike and having a power cord running down off my back… I hated everything about that. Boy was I ever wrong, and if I hadn’t built the solution and gotten on the bike and tried it, I’d still be just as wrong. This is something you have to experience to fully understand and appreciate.

The Good.

You are still tethered to the bike. But the smart setup mitigates this so thoroughly its unnoticeable when you ride and requires very little extra effort to deal with.

Not having the battery weight on the bike makes it behave… like a bike. Internet experts will jump up and down and point to the higher center of gravity that comes from putting the pack on your back. But reality is that without the weight of the battery, smashing thru a rock garden or challenging singletrack is like doing it on an unpowered bike. Since in singletrack you usually only use (or want) power when going uphill, that means your ride everywhere else is exactly like you want it: Old school analog. Your suspension acts like it should… but with a rider who’s eaten too many cheeseburgers.

Having the battery on your back means you can shift its weight from side to side just as you already do with your body. See the above point, because that one and this one together completely undo the whole ‘center of gravity’ argument, and put the backpack setup in the ‘superior’ category when it comes to all-around performance. If you are wearing a 10 lb backpack… so what? You spent the money to buy a pack with a completely form-fitting back panel, that attaches firmly to you so its an extension of your body. No shifting of any kind whatsoever. You did that, right? Bought the really good pack? Cuz if you swiped your kid brother’s lunch pack or figured out some other way to cheap out… you’re screwed. Proper packs are not just ones that shield and pad the battery. They shouldn’t fidget.

Holy crap I totally forgot about that cable! I thought that was going to suck so hard, and I don’t even know its there! Thats you after your first ride. My first config ran the cable around my side and did not go thru my legs. I was concerned (and rightly so) the cable could flop away from my side and hang up on a bush. So I took the plunge and ran it between my legs like the experienced builders say I should. Sure enough it works perfectly.

We have addressed the safety/crash issue by using a hardshell pack, with some dense foam around it but not smothering it (and used a battery cell that doesn’t heat up under extreme load). That makes the battery safer than it ever would be in a ‘traditional’ battery bag.

Do NOT forget to carry along a safety plug to cap your pack’s power cord when it is disconnected. I am using an extra XT90 male plug where I siliconed over the power leads (and I added another bead once I saw the gap in this pic)

The Bad.

You are still tethered to the bike. I never said a backpack was the best solution. Its just the only one sometimes. Its not the end of the world if you do it right.

When you stop the bike, you have to disconnect. Its not difficult, but you have to do it so it goes on the list. I keep XT90 safety caps in a little pouch and use them to cover the open connections on the bike and my battery cable. When I mount the bike, I first lower the dropper post all the way. Then I straddle the bike from behind, standing over the rear wheel. I connect the power and, since the seat is so low, I can just step forward and be right over it. I then raise the dropper and I’m on the bike. Dismounting I have some options. I can be standing and reach down, disconnect and just throw my leg over like usual, or do the reverse of the mount from the rear. In practice I’m about 50-50 as the rearward exit is easier but I need to think about it to do it.

And The Ugly

Whats ugly is I used that unoriginal cliche for those pro and con section titles. Lets take a break, sit down with a plate of spaghetti and enjoy the movie!

Quick Release, Easy-Carry Ebike Battery Setup

Parking your ebike outdoors all alone? When shopping, my cargo bikes are locked but out on the street… but the battery goes in with me. Here’s how I do it without people thinking I am carrying a bomb.

Yes You Can Take ‘it’ With You

An ebike used for utility purposes is, by its nature, going to be left out a lot. You go to the store, load up a shopping cart, come back and fill up your saddlebags. You really want all the parts on the bike when you left to still be there. Especially after loading on 50 lbs of cat food, Oreos and diapers.

The most obvious way you keep the bike itself is to use a good locking strategy. I’ll save that for a different discussion. This time I will focus on how I protect the single most-expensive component on any ebike – the battery. Not by locking it up, but by making it so I can do a quick grab and carry it in with me.

By removing that battery, we are making that big heavy ebike into a boat anchor, which we can hope makes it at least a little less attractive to thieves.

Size (and Shape) Matters

What I am describing can be made to work with any shape battery, kept anywhere on your bike. What you see here works best with a squarish, oblong battery. In the pics below I am using a 17.5ah Luna Storm battery, which is pretty big and heavy (in part thanks to its powerful but not-so-energy-dense 25R cells). More likely, if you have a similar heat-shrink battery pack like this one, its quite a bit smaller and lighter.

I also keep a Luna Wolf Pack battery like this and do not use its magnetic mount. The battery is easy to quickly get off that mount, but leaving it inside of a bag like I describe here is, overall, easier than stuffing it in every time, taking it back out and so on. For packs like this (Wolf, Shark, Dolphin etc.) you could certainly bring a small pack and put it in/take it out as a part of your routine.

There’s more than one way to skin this cat, so what you see here is just a jumping off point.

Lets Get to It

This is the battery in its bag, just like it would be if I rolled up to the local Costco.

Ignore the charger cable in the front. I took this pic at work in my ebike garage.

If we zip open the bag, we don’t see a battery. We see an inner bag, along with that charger cable extending thru to the rear. The controller cable is in there too just out of sight (look closely and you can see it)

If we look inside the bag, we see the battery charge cable is in fact an extension running from the rear of the interior bag up and out the front. The motor cable – an XT90S connector – also has a short extension between the battery cable and the motor cable. The idea is this: when routinely, frequently detaching and reattaching the cable, if there is any wear its on a cheap, replaceable extension and not a critical, live/hot cable coming directly off the battery.

Disconnect the cables and give a tug to the inner bag. Here its shown halfway out but you will just pull the thing out in one motion.

When I leave, I generally put the cables back inside and zip it only halfway-ish, so its obvious there’s nothing worthwhile to steal inside. Move along.

Annnd here we are. the cables are shown sticking out of the inner bag. You will want to cap those for safety’s sake. I use cheap plugs I got a bagful of on Fleabay for a couple bucks.

And yes… as-is I have had someone ask me “what is that a bomb?” … only half joking and ready to clock me if I make a sudden move. So stuff the wires in the bag so they don’t stick out.

Done! Wires are capped and stuffed into the bag in 5 seconds. The sling strap goes over your shoulder for easy carry. I just lug it to the nearest shopping cart and put it in the bottom rack with my helmet and off I go.

This is just a 3L hydration bladder pouch, the sling strap that comes with it and a shoulder pad I swiped off another strap I wasn’t using.

Parts

Its a really short list with one item on it.

Hydration Carrier

You see above the Blackhawk S.T.R.I.K.E. carrier in use. Purchase link is here. Yes, the name is a tad ridiculous. But this pack is minimalist and is just durable cloth with no insulation or padding. Its easier to stuff into a confined space. Mine came with a super sturdy velcro sling strap.

Another that is well made (and a tad smaller for a tighter fit is sold by Voodoo Tactical. It comes with thin backpack-style shoulder straps that don’t take up *too* much space in your triangle bag and are not enormously fiddly when stuffing back in there.

Another one I use (with my Luna Wolf pack) is this government-issue USMC carrier. The link is to a brand new unit. I got mine surplus and cheaper on Fleabay. This pouch has no straps (you can clip on your own from a duffel bag if you like) and it is the opposite of the Blackhawk carrier: Its thick and padded. I can still stuff it into any triangle bag I have despite this. Its great as a protective layer over a battery.

Wrapping It Up

There are lots of ways to do this. How I do it is no big deal. Key takeaway here is to find a method that works for you so you can swiftly grab the battery, go off to your next adventure and then come back and plug right back in again.

Li-Ion Ebike Battery Charge Charts

Whats an 80% charge on a 48v battery? on a 36v? 52v? These charts give answers to questions like these on all common ebike battery voltages.

Remember, ALL numeric charts show ballpark values that may be numerically correct, but no generic chart can match your individual cell characteristics, your pack’s age or its chemistry. Bottom line: imperfect charts like this are still good baseline references. Use these and teach yourself how to read the voltage gauge on your display screen.

Quite some time ago, I produced a series of charge status charts for a variety of common lithium-ion battery voltages. They’ve become a fairly common link to help folks out on various Facebook groups who use these battery voltages in their ebikes.

I built them using Google Sheets, so they are not web pages, which I suppose has kept them from being widely linked in search engine results when people are looking at such things.

Here for the first time are direct links to the charts on a normal web page.

36 Volt (10S) Battery Charge Chart

The first link is to the lowest voltage: 36v. Generally this is the lowest voltage you will find on a modern, commercial ebike. Note that its called ’36 volt’ but really that is the ‘nominal’ value. A 36v battery is actually fully charged when it is at 42.0 volts.

Click on the image above to be taken to the actual 36-volt battery charge chart.

48 Volt (13S) Battery Charge Chart

The next common size is 48v. These batteries are fully charged at 54.6 volts.

Click on the image above to be taken to the actual 48-volt battery charge chart.

52 Volt (14S) Battery Charge Chart

The next battery voltage is 52v and very common. 52v batteries will work on systems designed for 48v, and why is easier to understand when you become aware that a ’48v’ battery really tops out at over 54 volts. A ’52v’ battery tops out at 58.8v, so it essentially lets you use a 48v system for a longer time at higher voltage levels that it is already designed to utilize.

Take a guess what you are supposed to do to see the 52-volt battery charge chart.

60 Volt (16S) Battery Charge Chart

With a 100% charge voltage of 67.2 volts, when you have one of these you are getting into high voltage territory

72v (20S) Battery Charge Chart