My iPhone 4s automatically turns after every 10 mins when connected to a 3G Network

Hi,

I'm now having a problem with my iPhone 4s.

At first it will turn off when my battery is already at 20% now its worst because it will automatically turn off even though my battery is at 37%.

I just realized that it only happens when I am connected to a 3G network. I haven't experience this problem for more than a year until now. 😢

Can anyone please help me??? By the way, i tried resetting the network but it doesn't help.

Thank you.