mAh capacity

[Frenchfry1942]

Without looking at the outside of a battery, is their a way to determine the mAh rating? Assuming it is fully charged.

 

[Mooch]

The typical method is to draw a constant amount of current from the battery and time how long it takes to drop to a certain voltage. The capacity (at that current level) is then calculated by multiplying the current, in mA, by the number of hours it took. That gives you the mAh (milliampere-hours) capacity rating of the battery.

If you have a particular mod you know how long you can use without changing (or recharging) batteries, you could put the unknown battery into that mod and see how long it lasts compared to the other battery. Not very accurate but would work in a pinch.

If you have an 18650 flashlight you can can compare the unknown cell to another one you know the capacity of. Just compare run times. Or use anything that might run at 3V-4V, perhaps small bulbs?

Start slow with the current level you select though and check the cell every few minutes to make sure it's not getting hot.

[edit] Hmm...Just realized that the battery may not be accessible at all to put into another device of one kind or another. If so, can you estimate what the current draw is (for whatever it's in) and/or the load (resistance)?

 

[Frenchfry1942]

Okay, thanks. The concern for re-wrapping just got me thinking on it.