Can I insert 1 more battery cell into my iphone 3GS to increase battery life?

Hello people,

My iphone 3gs discharged battery very quickly, just after 1 day, from 7:00 am till 3:00 pm, so I had to recharge it very often. Recently I have had the batter changed but the result is not much better. The tech guy said that the circuit crashes therefore the batter discharged quickly and advised me to repair. I didn't agree because he is not Apple people and not trustworthy but just had him change new battery, I have no idea whether or not he has cheated me as he took my phone into his private tech room and came out giving me back my phone, saying the battery replacement was done, I paid him about $12, he even didn't mind of returning me my removed battery till I asked, he may have wanted to keep my error battery to cheat the others. He is not professional and kinda cheating. I suspect that he may have sold an old battery to me . I wonder if there is enough space inside the iphone case for me to insert my removed battert cell so my phone will increase battery life with double cells. Is it possible>?

Wilson