Siemens S40

Ok I did a search and didn't find an answer to my problem, so here's the question
When I recharge this crappy phone the battery recharges but it only lasts for maybe 2 minutes, I have allready ordered a new battery but what if it isn't the battery that's crapping out on it, what do u guys think the problem is? I'm only asking this question because I'm selling the cellphone but need to fix this problem before I sell it Thanks for the replies, later