What is "full" charge?
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I mentioned a few weeks back that my HP notebook won't charge its battery if
its "charge state" is 95% or higher. This prevents the battery from receiving
a "full" charge until the charge state has dropped below 95%.

I normally leave the unit on charge, knowing that it can't be "overcharged". I
checked earlier today, and sure enough, the charge system reported 97% -- and
the battery wasn't being charged. That's as it should be.

At least one poster has stated that leaving a Li-ion battery at continual full
charge will damage it. But what is full charge?

http://www.batteryuniversity.com/lea..._ion_batteries

According to this Battery University article, "full" charge occurs at a
nominal 4.2V/cell. At this point, the charger is supposed to completely shut
off, with no trickle charge (not unlike a lead-acid battery).

It would appear, then, that with a /properly/ designed charger, overcharge is
impossible. It's safe to leave the charger plugged in indefinitely.

The following remarks seemed pertinent, though...

"If a lithium-ion battery must be left in the charger for operational
readiness, some chargers apply a brief topping charge to compensate for the
small self-discharge the battery and its protective circuit consume. The
charger may kick in when the open-circuit voltage drops to 4.05V/cell and turn
off again at a high 4.20V/cell. Chargers made for operational readiness, or
standby mode, often let the battery voltage drop to 4.00V/cell and recharge to
only 4.05V/cell instead of the full 4.20V/cell. This reduces voltage-related
stress and prolongs battery life.

"Some portable devices sit in a charge cradle in the on position. The current
drawn through the device is called the parasitic load and can distort the
charge cycle. Battery manufacturers advise against parasitic load while
charging because it induces mini-cycles, but this cannot always be avoided; a
laptop connected to the AC main is such a case. The battery is being charged
to 4.20V/cell and then discharged by the device. The stress level on the
battery is high because the cycles occur at the 4.20V/cell threshold.

"A portable device must be turned off during charge. This allows the battery
to reach the set threshold voltage unhindered, and enables terminating charge
on low current. A parasitic load confuses the charger by depressing the
battery voltage and preventing the current in the saturation stage to drop
low. A battery may be fully charged, but the prevailing conditions prompt a
continued charge. This causes undue battery stress and compromises safety."