I sent the previous message from MS Exchange operating under a web
browser. It apparently mangled it. Here it is again sent a different
way.
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My knowledge of this comes partly from personal experience and partly
from lots of reading of various sources. Nonetheless, there seems to be
considerable confusion, and I do not claim to have perfect answers.
It seems clear it is better to discharge NiCad batteries nearly
completely before recharging. Otherwise they suffer what is referred to
as a "memory effect" that reduces their ability to deliver a full
charge. Some NiCad rechargers can be set to further discharge a
partially discharged battery before charging it. This is generally
known as "conditioning" the battery.
It seems clear it is not good (indeed very destructive) to completely
discharge the lead-acid battery in your car. A single case of complete
discharge can ruin the battery.
It is not clear that the degree of discharge before recharge has much
affect on the lifetime of NiMH batteries or Li-ion batteries. Most
sources say these batteries do not suffer a "memory effect" and can be
deeply cycled or shallow cycled without long term consequences.
Nonetheless, the batteries do have a finite number of cycles before they
need to be replaced. The point is that this number of cycles does not
seem to relate nearly as much to the depth of discharge for these
batteries as it does for NiCad or lead-acid batteries.
I have a fairly large number of NiMH batteries I use in a digital
camera. CD player. GPS, Celestron Telescope, etc. I have run
charge/discharge cycles on these in which I have plotted (with a chart
recorder) many charge discharge cycles under various depths of
discharge. I have not been able to discern any pattern that seems to be
better or worse for these batteries, so I am inclined to believe the
advertisements that claim you don't have to follow any particular
regimen for these batteries.
I am using a recharger specifically designed to recharge NiMH batteries
(Maha is the manufacturer). Rechargers specifically designed to
recharge NiMH batteries recharge at a high current, then switch to a
type of trickle current when the battery is nearly charged. But it is
more complicated than that. The microprocessor initially charges the
battery with a high current that is pulsating. Then it switches into a
steady mode and monitors the voltage over time. When it detects a
voltage peak it goes into a "trickle mode" in which it alternates no
charging with low charging (rather than a continuous low-level
charging). It is something in the neighborhood of 10 minutes of no
charging cycled with 2 minutes of trickle charging.
This shows that battery manufactures are playing with recharge methods
in an attempt to squeeze out more recharge/discharge cycles before the
batteries needs to be replaced. In my experience they are having some
degree of success with NiMH batteries. I do not have much experience
with Li-ion batteries.
Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton College
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu