Hi it's a great idea to change your battery and at the same time you can fit a higher capacity one. My old 3S was hard on the battery after a OS update and the advice I found was to disconnect the battery and reattach it to recalibrate the phone, so I thought I would update the battery at the same time. It can be done easily yourself but my eyesight let me down, picture trying to reconnect the small plugs and holding a magnifying glass at the same time. Any way my niece has had the phone for the last year and battery life is still great. Cheers, Ken.