well i let mine get down to 5 percent then i charged it but this morning i am going to let it completely die to where the phone cuts off and then charge it to 100 percent.
There are many schools of thought on this. I usually follow the school of thought to let the battery completely die, then charge it to 100% while the phone is off a few times. Don't know if it really does anything. I'm pretty sure that, as far as the battery goes, there's no "memory effect" as in NiCd batteries. I've heard talk that the phone will learn a better calibration after doing what I've mentioned a few times though.