Quote:
Originally Posted by JSWolf
So it's not true that lithium-ion batteries have a certain number of charges and when you have to charge more you get less time with the battery before you can tell it isn't holding as much power?
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It's not true. That's not how lithium-ion battery chemistry works. There is no counter, as you seem to believe. Amazon are not idiots and did actually design this thing to not die after a year and piss all their highest-spending Kindle customers off.
What happens is that *deep discharges* and the resulting long rapid charges cause plating of lithium metal on the electrodes (anode or cathode depending), and once it's plated it drops/flakes off and, well, there's no way to get that lithium metal back into ionic solution again, so the capacity of the battery drops. For most Kindles, this is how the battery is usually used unless you really like recharging it, but not the Oasis internal battery. Short, frequent charges and discharges of a mostly-full battery -- the predominant mode of use of the Oasis internal battery -- have very nearly no effect on battery life. There *is* an effect, but we're talking so many tens of thousands of charges and discharges that I haven't been able to find any research that has driven it to completion with, say, 10% or 20% charge/discharge cycles: they let it drop about 20%, enough that they're not guessing too much at the shape of the curve, and extrapolate. This does not affect internal voltage levels of a non-full battery, so what you see is that the battery appears less than 100% full when it is actually full: the battery seemingly won't charge all the way any more.
At shallow discharge levels, the effect of plating is probably much smaller than the slow internal resistance increase caused by simply keeping the thing in an oxygen atmosphere (that's the effect that causes it to run out of power when there's still 30% reported as left, or whatever -- though in practice battery circuitry will compensate for this, but if it didn't that's what you'd see). It starts getting significant if you drop the battery to maybe 30% total charge on a frequent basis: 50% seems to be fairly insignificant, but as you can tell from the woolly wording the data is very fuzzy at this point and is confounded by all sorts of factors.
So given my Oasis usage patterns (replace in cover while not using, internal battery fluctuating around 70--95% charge) I expect to have to replace the *cover* due to plating eventually (I never bother to charge the thing until the cover is nearly empty), but the Oasis itself? Naah. The battery will die after a decade or so from internal oxidation, only by then it will be totally obsolete. Say rather that obsolescence will cause me to replace it, not battery capacity loss.