My VERY limited understanding is, the problem isn't "overcharging"
exactly.  It's that Li-Ion batteries are weird.  They last longest when
charged between 50% and 80% - as opposed to 100%.  But bad news:
maintaining the battery at a level below 20% is just as bad as keeping it
at 100% if not worse, so...leaving it out really isn't a good solution
either.

What we REALLY need is a switch or setting in the laptop that will cause a
100% charge when you know you'll need more battery life soon, otherwise the
default charge level is maintained at around 75%.  But that would confoose
too many people...might be a good FOSS project for geeks though?

Failing that, the best solution is to leave it in there.  Yes, the battery
will slowly degrade.  But, at least you have protection from a sudden crash
if you accidentally the power plug :(.  If you can afford it, run two
batteries - swapping once every week or two (or however long it takes for
it to naturally drain to about 50%), with the one about to go on the shelf
being deliberately drained to about 80% first.

Jim

On Sun, May 6, 2012 at 4:17 PM, Robert Holtzman <holtzm@cox.net> wrote:

> For the record, I'm running a Lenovo T420i with a 6 cell battery.
>
> In the past I've been told that it's bad practice to run a laptop on AC
> with the battery installed because it would cause reduced battery
> capacity. This raises two questions. First, is it true that laptop
> batteries don't have overcharge protection, and second, how many cycles
> is a battery like mine good for?
>
> --
> Bob Holtzman
> If you think you're getting free lunch,
> check the price of the beer.
> Key ID: 8D549279
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