NiCd Battery Questions

ransley wrote:
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They say to discharge NiCd batteries before recharging to avoid the "Memory Effect".
However, there are 2 effects of NiCd - "memory" and "voltage depression".
The latter is avoided with faster charge time "smart chargers" that detect "full charge". Overcharging a NiCd reduces its voltage by 4% or so, but that is often repaired by full recharge after full discharge.
The former is actually less of a problem, mainly cropping up if partial discharge to same extent as before followed by recharge is repeated to great extent.
Meanwhile, overdischarge of NiCd batteries appears to me to be the main cause of damage.
If you have NiCd batteries, I find best so far for a "maintenance proceedure" is to discharge them until they have voltage "in an earlier stage of going downhill" due to approach to full discharge, and then fully recharge them.
They should also be recharged if not having any recharging in the past year, maybe 6 months. I think more like 6 months for NiCd if recharged by a "smart charger".
Rechargeable batteries do not last forever no matter what you do. If you get them to be useful for 7 or 10 years, you are doing well.
One more thing - chargers with instructions to charge for 14 hours or anything more than 8 hours appear to me to be mostly "dumb chargers" that have a high rate of achieving significant overcharging. That "should cause at most minimal damage", though can cause the above "voltage depression" in NiCd and, if repeated frequently, can shorten life of NiCd and especially NiMH. If you want to guard against this, get a voltmeter connected to the battery pack while charging it - if it takes a rise from a stable level around 1.26-1.3 volts per cell to something higher and then stabilizes or "peaks out", then the battery has been fully charged and is being overcharged. Watch out for a series of alternating voltage stabilizations and rises as each cell in the battery achieves full charge at a different time - I find better to get all cells fully charged at expense of mildly overcharging some cells.
NiMH has no "true memory" and much less than NiCd of "voltage depression", but appears to me to be aged more by overcharging than NiCd is. However, damage from overcharging of NiMH appears to me to be small enough to be better worth charging a "series pack" until all cells are fully charged as opposed to charging until one cell achieves full charge.
I actually like "smart chargers" of kind that achieves small extent of overcharge due to delay of detection of full charge - by detecting directly (with a temperature sensor) or detecting indirectly (voltage peaking out and then decreasing, apparently-to-me as result of temperature rise) that results from overcharging. I like such "smart chargers" for actually minimizing overcharge in comparison to "dumb chargers". Such "smart chargers" tend to have charge time 4 hours or less.
Bottom line - it appears to me that if rechargeable batteries are "optimally babied", they last maybe 7-10 years and occaisionally more, and if "used reasonably well" they last 5-7 years.
I would not fret about minor to moderate deviation from "whatever is optimum treatment" for rechargeable batteries, since they will die and need to be replaced anyway - they will degrade at some rate or another no matter what you do! I think better to have them have a well-utilized good life and not fret too much! If you get both at least 4 years and 200 discharge-recharge cycles with a rechargeable battery 1/3 as good as new (in terms of time supplying "sufficient voltage" to the load, at least 1 or 1.1 volts per cell) afterwards, I think you are doing well!
- Don Klipstein ( snipped-for-privacy@misty.com)