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.