Battery

Lately my cell phone has been acting up. Ringtones go off, I think I'm getting a call, there's not one. Some calls don't ring, messages come through hours after being received. I believe it has to do with the battery. It's the same one I've had since I got the phone three years ago. It doesn't seem to hold a charge for long. If I use the phone, it drains the power within minutes of use. I suppose I should get a new battery or upgrade the phone, but I like my phone, and I am lazy, don't want to deal with, salesmen or contracts. Eventually I will do something, once I become annoyed.