[Discuss] [ OT ] iPad battery

[Rich Pieri]

On Fri, 28 Dec 2012 20:04:42 -0500
Jerry Feldman <gaf at blu.org> wrote:

> Basically in general the worst thing you can do with a Lithium Ion
> battery is to run it all the way down, and most systems with shut down
> at about 20%

Actually, this is the second worst thing you can do with a Lithium
battery pack. The worst is to leave it charging all the time:

* Plug into charger. Monitoring circuit charges battery.
* Battery reaches full charge. Monitoring circuit stops charging
  battery.

At this point if you don't disconnect mains power then the battery is
not used to power the device. The battery pack will still self
discharge all the way to zero given sufficient time, typically 2 to 3
months. The battery monitor circuit detects no drain on the battery so
it must still be at 100% and, since there is no power in the battery to
operate the device it will remain that way forever. Irreparably
destroyed battery pack.

The last time I saw this in action was about 8-10 years ago. Had a
little notebook playing firewall. Left the battery pack connected as an
ersatz UPS. When the power really did fail, so did the notebook.

Monitoring circuits are supposed to be "smarter" these days but better
safe than sorry. Don't leave it plugged in all the time. Use the
battery. That's what it's for.

-- 
Rich P.