Don't work on any electronic device without first making sure all the electricity in your body has dissipated. If you don't, you risk transferring the electricity inside of you to sensitive components. So, instead of saving a few quid changing out a battery in your phone, you end up having to spend a couple of hundred quid on a new phone. Yes, it really does happen.
Get one of these wrist bands that control where that electrical discharge goes, so it doesn't end up damaging your electronics.