NiMH discharge question

In sets of NiMH cells that are of a given lot (and even the same package) are you always going to have those that are weaker and poop out before the others, resulting in significant cell reversal? Granted, these aren't matched sets, but you would think from within the same lot they would be pretty close. Under load, I have three that still measure 1.05-1.10 volts, while a fourth is on its way down to zero as I test it. Open-circuit voltage (probably meaningless) places the four cells pretty close together.

in the same lot I have easily seen 10% capacity variance and about 5% voltage variance

You should be able to avoid cell reversal by recharging (or swapping batteries) at the first sign of weakening. Unlike alkaline batteries, NiMH and NiCd batteries maintain a relatively constant voltage until they are almost depleted. Some regulated flashlights, such as the Arc LS, make this easy for you by dropping out of regulation at this point.

Thanks for the replies! I keep spares handy and usually swap out my sets before they start to die anyway, just thought I would ask.

Arc First Run LS1's, with 1 AA, or 2AA body, and MM sandwiches will drive NiMH's way below safe discharge limit if you are not careful.

Bill

I run a BB400 with my NiMH cells, so the 1.6V hard cutoff should be safe. I swap the cells every 2-3 days, which normally is well before the charge expires...if I notice the module fall out of regulation, I immediately discontinue use of the light or swap out the cells.

The only problem I have run into is non-regulated fluorescent lights (such as the Energizer TrailFinder LED, similar to the Arc White) where you really can't tell the difference between a charged NiMH set or a discharged set just by looking at the CCFL. I guess I should adopt the same swap-out scheme on these as well. /ubbthreads/images/graemlins/smile.gif