IPod touch 5g battery issue

Recently, I updated my ipod touch 5g software to ios 7. Since then, when i charge my ipod touch, it takes only 2hour to fully charge and sometimes 1 hour 30 minutes. Before i update the software(ios6.1.3) it take 4 hours to fully charge and can use up to a day. But with ios 7 it drain a lot of battery and charged two times faster than usual. I wanna to make sure that if this issue is cause by the software (ios7.0.4) or is my ipod touch's battery had spoilt. Anyone have the same problem??