You are absolutely correct. there is no decernable "memory effect" with NiMH batteries. There is decernable loss of capacity (and therefore life) with continued use. Internal resistance builds up. This was quite a problem with NiCds, but they could be reconditioned. All geostationary spacecraft using NiCds (old days) put their batteries through reconditioning just before eclipse seasons. This involves draining the battery at a specified slow rate relative to the AH capacity until a specified very low voltage. The battery is then recharged at another specified slow rate until fully charged.
With NiMH batteries, the AH capacity remains high (decreasing slightly) until near the end of life when the capacity drops dramatically. NiMH batteries and reconditioning are like old men and sex. We can live without it, but we like it if we get it. 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. All batteries do better with a slow charge. Fast chargers are for when you don't have a choice and need your battery ASAP. 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. Regards, Bob Blakely --------------------------------------------------------------------------------------------- "A mother takes twenty years to make a man of her boy, and another woman makes a fool of him in twenty minutes." - Robert Frost ----- Original Message ----- From: "Cory Papenfuss" <[EMAIL PROTECTED]> > Pretty much correct. The "memory effect" is almost completely a > myth... it was only prevalent on 1960's/1970's vintage NiCd cells under > automatic cyclic charge/discharge cycles used for NASA robots, etc. The > much more common cycles are series cells repeatedly cycled and having some > weaker cells getting progressively more undercharged and abused. The > other common failure mode is people so worried about memory effect that > they keep cells on trickle charge for storage. It promotes other problems > that reduces capacity. > > I've got some cheapo NiMH AA's (2150 mAh) that only last about 50 > frames in my -DS. Once I got some good quality Energizers, it's more at > about 500. I also invested in a GOOD battery charger (LaCrosse BC-900) > which charges cells individually, as well as being able to give valuable > feedback on capacity, discharge, variable charge rates, etc. Bottom line > is with good quality NiMH cells and a good charger, they work fine. If > you haven't used the camera after a month or so, you may only get 50% if > you don't top them off first. Still... not a bad tradeoff. -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
