It is time to get a new battery when the battery is not performing as you expect it to. When it is holding charge for half the time it once did or it gets very warm doing the simplest of tasks. The time it takes to get to this point will be different for each user based on usage and how the unit has been charged. For best results charge the battery as slow as you can and plug it in when it needs it and remove it from charge when it is done. Do NOT put it on charge and leave it there until you go out the next day if the cell needs an hours charge then give it an hours charge.