LG Viewty Battery Problems.

[Mueymue]

Within the last week, my phone has started doing really weird things!
Basically whenever I use the internet, no other time, the battery instantly drains! Today I had it on charge, I unplugged it and went online and it started beeping for low battery literally within 5 mins! It is extremely frustrating as the internet is one of my main uses on my phone! I've tried a hard reset and I've just restored it to factory settings, but so far no luck!
It doesn't even drain when I'm on the phone for ages, only when I'm on the internet! And then if I come off the internet, the battery goes straight back up to full battery life and it stops beeping!
Can anyone think of any way to resolve this? I'm on a contract phone but I can't upgrade for another 8 months! And as I got it at phones 4 u, if I send it away to get it repaired, I have been told I DON'T get a replacement phone in the meantime, it'll take two weeks to repair and I have to send it away 3 times before I can get a replacement, so if worst comes to worst, I have no phone for 6 WEEKS!

Help!