HT1476: iPhone and iPod touch: Charging the batteryLearn about iPhone and iPod touch: Charging the battery
Currently Being ModeratedNov 26, 2013 6:10 PM (in response to jeremiarg)
Once your battery reaches 20% you have basicly "reset" the battery.
Some people take it lower but I don't think it's nesassary.
This is supposed to condition your battery and promote longer life.
Currently Being ModeratedNov 26, 2013 6:23 PM (in response to jeremiarg)
The battery is a lithium type one. One of the many advantages of a lithium battery is that is doesn't build up a memory of it's high and low points. Consequently you can charge it whenever you want to knowing you are not going to damage it.
However, having said that, some manufacturers recommend you should periodically allow the battery to completely drain then charge it overnight. The battery has a chip which prevents it from going completely dead as a lithium needs to have a minimal amount of charge to stay alive, if it goes beyond that point the battery dies.
All batteries will eventually die and a rule of thumb is that most batteries operate to an optimum level up to 600 charges. Anything beyond that is when you will notice the battery does not hold its charge as much as it used to.
Best advice I can give is just to charge it when you need to and allow it to completely discharge once every 3 months and charge it overnight.