Yeah, the proper way to charge a lithium-chemsitry battery is pretty-simple, but NOBODY does it (including LG).
It's this:
1. Charge at up to 1C (that is, if you have a 3,300mah battery, 3.3 Amps) until the cell voltage reaches 4.2V. This is 85% of capacity, approximately. From "empty" this will require about 45 minutes, assuming you can source sufficient current and the battery doesn't get hot.
2. Hold the charge voltage at 4.2V. Charging current will taper; when it gets to .03 C (e.g. ~100ma) the cell is full. This will require about an additional *two hours*.
A cell that exhibits more than a roughly ~20F rise in temperature during charging *before* its terminal voltage reaches 4.2V is compromised and should be replaced. The device *should* display a warning if that happens (note that no existing cellphone does from LG or anyone else.)
If the device is on during charging then you have additional problems determining the actual rate of charge because you must accurately measure the drain of the device and subtract it from the charge current. You must also account for cell heating from the device and charging circuits when monitoring the cell temperature if you are attempting to alert on a defective battery due to high resistance.
A phone company that actually cared about its customer experience would offer the following settings when it comes to batteries:
In ALL cases -- any cell below 3V is charged at 0.1C (~300ma) until the voltage reaches 3V. This should NOT happen (such a battery has been "overdischarged") but it can, and the only safe alternative to the low-rate initial charge in this case is to declare such a battery "dead" and refuse to charge it at all.
1. "Preserve battery life" (default): Charges to 4.2V at all available current levels up to 1C, then shuts off. No saturation charge; if left plugged in will hold voltage at 4.0V, assuming that temperature remains within limits. This will result in a battery charge to 85% very rapidly (assuming it doesn't get hot), but essentially no charge at all beyond that point. If you select this you'll more than *double* battery cycle life over what cell companies do to you now.
2. "Fully charge consistent with good battery life": Charges to 4.2V at all available current levels to 1C, then holds at 4.2V until the charge current drops to 0.03C and terminates. If left plugged in will re-start when voltage drops to 4.0V. This cycle is a decent compromise, will charge to 85% from effective 0% in an hour but requires ~2-3 hours to reach full charge. This will result in roughly a 50% improvement in battery cycle life over what you experience now.
3. "Fully charge and hold": Displays a warning about compromising cell life if selected. Charges to 4.3V before tapering. Far more likely to run into heat-limiting during the charge; will charge to 85% in an hour but "finish" in another 20 minutes or so. Holds the cell at 4.2V if left on charge. This is pretty-much the protocol that cell companies use now, and it does fairly severe damage to cells if frequently charged fully (resulting in about a one-year service life instead of 2-3.) This is what you get now.
If the unit is OFF during charging then
#1 is used with the modification that no float current is applied at all, nor will charge restart, until cell voltage drops to under 3.6V.
LG appears to add a twist to
#3 in that it immediately current-limits the charge to about 700ma if the screen is on. This is arguably a good practice as it limits some of the damage that
#3 does especially in a car where you have the phone connected to power and are using it for Nav; most phones will immediately run the battery up to 100% under fast-charge in those conditions, limited only by heating, and that's really, really rough on battery life. It also appears LG cuts off the charge short of the 100% level (at about 95%) which is also good. But they could do better if they implemented the above.
If manufacturers had any interest in actually providing you with all the cell life you bought originally they'd allow you to select
#1 and maybe default to
#2 . As it stands they all do
#3 , some with a few twists. LG is one of the few I've seen that actually tries to mitigate *some* of the damage by limiting charge rate with the screen on and cutting it off a bit early if left plugged in.