replaced battery, indication 100% charged, but battery is empty

I have just replaced the battery from my iphone 3gs and I connected it for recharging, the screen came on and showed 100% charged and asked to connect it to i-tunes. However, when I disconnect my iphone is dead (which makes sense since I did not charge the battery yet. I guess as it shows 100%, it won't charge either. Any suggestions?

Many thanks