My nokia 5800 keeps crashing can you help me fix it?

Hi there,

My Nokia 5800 keeps crashing and the battery life seems really short (running down nearly every day after appearing fully charged). Do you think its a faulty battery thats causing the phone to crash and the battery life to be short, or is it an error on my phone thats making it crash and running the battery down?

If its the battery I could try changing the battery but I'm not sure thats the problem.

Any advice would be really helpful thanks

Jacob