i juz got my o2 atom(2nd hand), I charge my battery abt 3 hours. but it still canot on. what happend to my battery?

Hi, I was wondering is any1 having the battery problem wif their o2 phone? I recently bought a o2 2s(2nd hand), the 1st day go well and the battery is rechargeable. But the problem came at 2nd day when the battery run out,I cant charge my battery anymore (i.e. the battery signal light is on and it stated is charging but few hours it stiill 0%). so, i took my o2 back and the seller replace another 1 to me, o2 atom. The same thing happend to this phone. So, I took it back again and he say will change another o2 atom to me 2morow. Anythig wrong wif those o2 phone? Is the shop selling faulty device or is my problem? Please advice me. thank you