Calculating usable battery capacity

[Laen]

usable battery capacity

I have a question about battery capacities and the actual usable work I'll be able to get out of them. My question is specifically about a lithium ion/poly battery pack, but I'd be interested in how it works for other chemistries as well if there's a difference.

I have a LiPoly battery pack labeled "3.7V 2000mAH". When its fully charged, it's 4.2V, and that I risk damaging it if I drain it to under 3V. My question is, how many watt hours of usable power am I actually going to get from it?

Is the equation "( maximum voltage - minimum voltage ) / maximum voltage * capacity in amp hours" ? Or is there some other piece of information I need to calculate it?

Thanks in advance.

 

[yetisouth]

The Ah rating depends on the discharge current. The higher the current, the lower the Ah rating you get out of it. The relationship is complex, and differs for all types of Batteries. Here:

https://www.mpoweruk.com/performance.htm

is a better explanation, with sample graphs.