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.
48 Volt (13S) Battery Charge Chart
The next common size is 48v. These batteries are fully charged at 54.6 volts.
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.
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
Great looking charts, but I would like to ask a question. When charging my 36 volt e-bike battery pack it gets very hot at about 36 volts, even when pulled out of the sleeve. I turn the charger off and let it cool down then repeat process again until it gets hot with not much gain. About an later it goes down to 34.8 volts and seems to stay there. Checking each of the 24 cells they’re all 1.42 volts. My question is: would that be a short in a lithium battery? If so, how would I know which one it is, when they all test out at the same voltage? They’re all balanced or should I wait longer to test each one again?
A battery heating up during charging typically is – absent any other malfunctions within it – due to using too many amps. The bigger the battery, the more tolerant it is of fast charging (using a lot of current/amps). The smaller … the reverse. I would look into how many amps you are pumping into this battery, and how big it is. Or, in a pinch, just reduce the amps going in and see what happens. You can read the article in this blog on An Ultra Reliable Ebike Battery Charger to see how to go about making an economical charger capable of low current. If you have a lab power supply in your shop chances are you can work something up once you make a cable adapter.
Question from California: Would these values apply also to Lithium Ferro Phosphate batteries now widely used in solar storage systems?
I don’t believe so. Its close but not exact. These charts are keyed to the standard full and minimum charge values common to the garden variety 18650 and 21700 cells, which have a range from 3.0v to 4.2v per cell. My own home solar system uses LiFEPO4 cells and while I use the same chargers, I adjust them to the slightly different top end voltage.
Hey Matt, question for you on these battery charts. It makes sense that these voltage readings represent the charge level of the battery when the battery isn’t under load, but what about when it is? There are times where my 52V-nominal battery may be around 45-46 volts — call it 20-ish% charge remaining, but under a 10A load that voltage may sag down to 43.0V. I presume that’s okay and not catastrophic to the battery… this whole scenario is very rare for me in the first place. But where the charge says 42.0 volts == dead-and-damaged-batttery, what if the battery is just hitting 42.0 volts while under load and its no-load voltage is higher. Is that damaging?
Voltage sag like you describe is completely normal. Minimizing sag is one of the things you gain when you do big custom batteries. The more cells and cell groups you spread the load out over, the less sag. But, by and large, sag is just an item of passing interest. Unless you are draining the battery down low – which on general principles you should avoid – sag has no ill effect that you can do anything about. The only time it can affect your riding is if say you have drained your battery down low and you decide to ride up a steep hill under power. In that instance, voltage sag could take your battery voltage down to the point where your controller hits Low Voltage Cutoff and shuts the bike down. Cycling the controller (display) power will bring it back. If on the other hand its not the controller that pops but is instead the BMS, then IIRC you’ll need to plug the battery back into a live charger to get it to reset to normal. Which means you are walking home. So, moral of that story is to always set the LVC of your controller a little higher than the one in your BMS, if you can.
Ah, good points about BMS cutoff. Thanks for the thoughts!
> Which means you are walking home.
Or just riding under leg-power 😜 for most riders, anyway!