> The total life of a battery is drastically affected by both the depth of
> discharge it's forced to undergo and the rate at which it's forced to do it.
> Draining a battery until there's no juice left serverely curtails the
> batteries life. If I remember correctly, limiting the battery drain to about
> 60% depth of discharge is about optimal for greatest overall battery
> performance - but this also depends on many factors.
>
True for batteries, but not so much for individual cells. PbSO4
(lead-acid) batteries will sulphate if left dead for even a short period
of time, but NiCd and NiMH are OK with being dead. The trouble comes when
they aren't discharged individually, whether it's in a sealed battery
(cordless drills, etc), or due to chargers charging in pairs. There's
fairly strong evidence to support a roughly constant cycle x DOD lifetime
capacity for batteries IIRC. In other words, if one can run a battery
down to 50% and back up about 2x as many times as a 100% discharge/charge
cycle before their life is over.
> All batteries do better with a slow charge. Fast chargers are for when you
> don't have a choice and need your battery ASAP.
>
More efficent, certainly. Charging/discharging at 1C (e.g. 2.4A
for a 2400mAh cell) is only about 60% efficient. At 0.2C, it's more like
90%. As long as they don't get too hot though, it's not particularly bad
to charge/discharge them at high rates. Again... if *discharged* at high
rates in a long series string, individual cells can be damaged due to
voltage reversal from the other, stronger cells.
> A good NiMH charger will turn completely off when it has fully recharged
> your battery. If you need a trickle charger, you're not using your camera
> enough.
>
Exactly. Besides, if you've got a good charger and your batts
have sat for a couple of weeks, you can crank the current up and "top off"
rather quickly.
-Cory
--
*************************************************************************
* Cory Papenfuss, Ph.D., PPSEL-IA *
* Electrical Engineering *
* Virginia Polytechnic Institute and State University *
*************************************************************************
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