Battery Ah above spec with below spec draw?

[milkyspit]

As most of you no doubt already know, batteries are typically spec'd for a certain Ah capacity when subjected to a specific current draw. For example, Energizer AA alkalines are rated at 2850mAh for a 25mA current draw. (If memory serves.) It's also common knowledge that the battery's effective capacity DECREASES as current draw INCREASES. For example, an AA alkaline required to deliver a 300mA current flow will have an effective capacity of something substantially less than 2850mAh.

But does that also mean a battery might deliver GREATER than the rated capacity if current flow is BELOW the amount used for the rating? To continue the AA alkaline example, does that mean the cell might deliver substantially MORE than 2850mAh if current flow is only 1mA?

Is there any good way to estimate the effect increasing or decreasing the current flow will have on battery capacity, short of actually doing a real world test?

/ubbthreads/images/graemlins/confused.gif

 

[Brock]

I know that a lower draw does indeed give you more mA's out, but I don't know the ratio or "curve". I would think it would be not a lot more then at 25mA. I think once you get above this point with alkaline you start to loose more power to heat, while below that it doesn't heat up much at all.

 

[Ginseng]

Scott,

If you look at a set of discharge curves, the curves start to bunch up as draw current decreases. If you were to plot the attainment of a given voltage as a function of capacity, you'd see that they reach an asymptotic limit. That is to say, you would be able to extrapolate to a "zero ampere" capacity which would be the theoretical limit. It wouldn't be much practical use but would be interesting nonetheless.

Wilkey

 

[batterystation]

I ran those new Sanyo 2100 AA batteries on the analyzer here on a 48 hour discharge and got real close to 2400mah.
The bummer of a NiMH cell is the high self discharge. It can throw a real slow discharge way off because it can amount to a few percent a day.

 

[EvilLithiumMan]

Radio Shack provides a fairly comprehensive set of discharge curves (constant current and constant resistance) on all of their alkaline cells.

http://support.radioshack.com/support_tutorials/batteries/bt-alk-standard.htm