WynWins

I've had my G1 for about a year or two now and up until now I've had no problems at all with my battery besides it dying within like 4-6 hours (though I hear that's sorta common with new phones).

Over the past week or so though my battery has completely failed on me. I charge it for a few hours until the battery says it's full, then when I unplug it for about 30 minutes it suddenly turns off on me. It doesn't even say "Phone shutting down" anymore or show any signs that it's dying. The battery still shows green. I try to turn it back on which always fails so I plug the charger in then try it again and the battery is somehow already back at 70% charge. Does this mean I need a new battery?