Android and Linux

[richard.pieri-Re5JQEeQqe8AvxtiuMwx3w at public.gmane.org (Richard Pieri)]

Li-based battery packs are all in the category of "smart" batteries.  Unlike NiCd batteries which are charged by connecting them to a direct current, Lithium-based batteries have a dedicated charging circuit which regulates the charge voltage and temperature as well as monitors discharge through use.  This circuit also what reports battery state to the hardware it's powering -- so it isn't Android or Google that's doing what you see but the battery pack itself.

Li batteries self-discharge even when not in use, even when plugged in.  They don't trickle charge like NiCd and NiMH.  This bleed is *not* monitored by the charging circuit, can't be.  A problem with early model Li batteries is that if they are kept plugged in all the time the batteries would self-discharge to zero but the circuit would report a full charge and refuse to charge the battery.  Ker-broken.  The weirdness you sometimes see with charging states is extra logic designed to prevent this from happening.

There's wear and tear.  Each discharge of the battery pack slightly diminishes the effective capacity of the battery pack.  How much depends on how far down you discharge the battery pack.  300 to 500 discharges will reduce the battery pack to approximately 50% of the original charge capacity.  How many cycles depends on how much you use, with faster wear occurring if you discharge below about 50% of the original charge capacity.

On the other hand, you sometimes need to discharge the battery pack to recalibrate the charge circuit.  This one you should check the manufacturer's instructions because they do vary significantly.

Anyway, the Prius issue you describe is something utterly, completely different.  A problem with NiCd and NiMH batteries *is* overheating due to overcharging.  These batteries are made from a paste sandwiched between nickel plates. If they overheat, the paste dries out and the batteries are ruined.  Best way to prevent overheating is not to top them off.

--Rich P.