Does anyone know what an iPhone counts as a “full charge”? I plugged mine in and it’s charged up to 96% so far but the “time since last full charge” is already reset to 0 minutes. I would naively have assumed that it would have to charge to 100%…
There’s a circuit on the iOS devices (and most things with their battery type) that basically goes into a charge/discharge cycle when it gets near full. The battery can be damaged by charging past it’s full mark, so the circuit basically lets it drain a little, then recharges, over and over.
So it’s possible you were at 100 and are now down to 96 (although that seems extreme), or more likely that it considers a charge to 90 or 95% to be a “full charge.” Like most of those usage numbers, they’re more of an approximation than something you could take to court.
That’s probably it. I left it charging for another 20 minutes and it only crept up to 97%, so it probably considered the battery was full. (Although it usually reads 100% after a full charge.)
I believe the iPhone goes into trickle charge mode over 80% which may be the point it is considered full.
The 2nd post may also may explain why if I use a external battery to recharge the iPhone and stop it before 80% I can get ab out 2 charges on it, but if I let it go to 100% I get about 1 full charge.
I have NEVER heard of this being done while charging batteries, of any kind, and it would be damaging to the battery to repeatedly charge and discharge it over and over - after all, cycle life is a big factor in overall battery life. Real chargers simply stop charging the battery when it reaches full capacity (by measuring voltage and/or current, particularly for Li-ion batteries which are very picky about this and require special charging circuitry), or go into a trickle/float charge mode (depending on the battery type); there’s also no reason to switch to battery power while external power is being supplied.
While this is true of NiCd or Nimh battery it is not such a issue with Li-batteries which seem to be primarily effected by length of time at certain levels of discharge (with 100% being a life shortening level), with cycling a distant 2nd effect in battery life, and only used because it has become a standard do to the Ni-batteries.
I did find this page which mentions something similar to what TimeWinder said, but it seems to be a side-effect of poor battery management because it is harmful to the battery (just reading this makes me wonder how many of the reported battery fires occurred due to this sort of faulty charging process):
There’s no reason at all for this to happen, it sounds as if the device switches to battery power after it is charged, despite still receiving external power from the charger, which is clearly faulty operation. Note also that there shouldn’t be interference with battery charging with a properly designed circuit; I have found phone charging cradles that are nothing more than an AC adapter connected to a couple contacts; thus the charging is all done by the phone.