Iphone showing charge symbol but won't fully charge. Help!

[BoredHorse]

Hi,
Wondering if anyone can help.
I dropped my iPhone 4S a couple of days ago. The back of it smashed but the phone was still working correctly. I put it on charge that night and it was fully charged the next morning.
By the afternoon I put the phone on charge again as I had been using it all morning, the charging symbol shows but the phone is charging really slowly, going up and down in percentage. The maximum it will get to is 44%

Do you think I need a new battery? Do you think I have damaged something by dropping it?

I'm going to try using my friends charger later to check it isn't a charger problem but as I say, the charging symbol still shows up.

Just for extra info, I did update to IOS7 on Thursday and I have noticed my battery draining a bit faster since.

Thanks