Originally Posted by Szadzik
The fact that it does not discharge down to 0 does not mean it is good for the phone. These batteries are maintained in the best way if you do not go below 20% before plugging in. The advice, is harmful and if you follow it, you will kill your battery in a few days.
That is completely false. I'm not sure where you're getting your information or if you've tried it yourself, but I regularly completely discharge and recharge the battery in my S2 and I still get good life out of it.
Do a search for "battery calibration" - most sites advise that you discharge the battery completely, recharge completely with phone on, then turn the phone off and charge it further.
Manufacturers wouldn't let you deplete the battery below 20% if it was harmful to the battery (more harmful than ordinary use anyway).