Quote:
Originally Posted by mstevens
Everything I have ever read about lithium batteries suggests that this is complete poppy**** and that only nickel cadmium batteries suffer from significant "memory effect" (and nickel metal hydride ones only a little bit). However, I'm a doctor, dammit Jim! Not some pointy-eared electrical engineer!
I'll see if I can come up with another battery to see if it behaves any differently.
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I happen to be a pointy-eared EE. You are correct that the last rechargable battery chemistry to really have a memory problem was NiCad. That said, one of Li-Ion's biggest problems is a gradual slide out of calibration for the battery's internal circuitry. Essentially frequent shallow discharge and charge cycles make it "lose track" of what its total energy capacity is at the moment, as it tries to count incoming and outgoing electrons. There is always an error in this measurement thus over time the calibration becomes incorrect. A deep discharge re-calibrates a used battery (specifically the internal circuitry), but doesn't add capacity, per se. However, the symptom acts like memory for the most part, which is interesting.
I am not a chemist but it seems new Li-Ion batteries do indeed require a few discharge cycles before reaching full capacity, and I don't believe it is an internal calibration thing, either. I have seen this recommended in more places than this forum, and at least once from an OEM (PolyCom on their SoundStation 2W wireless speakerphone kit).
As far as life, Li-Ion basically wears down from total energy throughput, whether they are from shallow discharge/charge cycles or deeper ones. One caveat is they do dislike REALLY deep discharging but their internal breakers cut off before the battery can actually become damaged, so this is more academic. Li-Ion's main enemy is heat, which no TP owner wants to hear, but it is true. In that sense, since a long discharge and a long charge cycle tends to cause more heat than shallow discharges and recharges, deeper cycles are harder on the battery. But it may end up sliding out of calibration over time and require a deeper discharge to "remember" how much capacity it actually has (which always decreases with age). I also suspect, but have not confirmed, that the sophistication (or possibly presence?) of this calibration circuitry can vary across applications and manufacturers.
One thing I read a while back is the Li-Poly batteries used in PDAs seem to be more resistant to heat, and may even become more efficient at elevated tempatures.