Problems with MBP (keeps resetting time etc)

i'm a relatively new macbook pro user i havent had many problems, but its started to behave funny recently.

I turned it on, and it told me 'something' caused it to behave 'erratically' and the time and date was set to January 1st. It also forgot my WiFi password which it usually automatically connects to. I didn't think much of it until it happened again there now when my battery was low, the laptop turned off at 4% [usually turns off at 1%].

any ideas what could have caused this?