iPhone 3GS battery and firmware problems.

Hey Forum,
I am using iphone 3gs and i recently found out that my iphone battery is faulty, i want to ask u guys if under these circumstances, is it faulty?
Problems:
-Fully charged in around 3 hours from 20% to 100%.
-Recently found out battery decreasing quite quickly(i think so, not 101% sure)
, btw, i restored my iphone software for around 3 times in a row due to some problems and around 7 times in total. I am a kinda paranoid person and sometimes when something happen to my possessions i juz cant sleep because I kept thinking of it, so I just want to hear from you guys if something is wrong from restoring firmware and that it can cause harm to my phone.
And would be really grateful if you guys can help me out, thank you so much, i really need to put my mine at peace.
Thank you.
Regards
ALa.
MacBook 13-inch Aluminum(Late 2008) Mac OS X (10.6.4) iPhone 3GS 16GB