Originally Posted by matttye
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).
Battery advice is like a religion and Russian roulette. One is "This is what I wish were true" and the second is "It never killed me so it's also good for you". My religion will not permit me to completely deplete a lithium-ion battery, and I keep it topped off whenever possible. I never played Russian roulette and never intend too.