I have recently been experiencing very short battery life when using the phone for calls. One 5 minute call and my phone dies. I can have it on standby all day and quick synch 4 or 5 times and it does not seem to be draining at all, but one phone call and the battery is drained. Does it mean it's time for a new battery or is there some other problem? I've had the battery for about 2 years now.