Long story short.

Had my iPhone for about 2 years. Recently the battery started dying on about 19%, then it would just randomly die if it wasn't plugged in (would only survive about 10 minutes unplugged).

So I purchased a new battery off a reliable TradeMe user (Had over 10k Positive rating for selling iPhone and phone parts)

So I have put the new battery in..

BUT,

Now my phone doesn't turn on at all. It turns on if it is plugged in to a charger and shows 80%. The 3G and wifi comes on, also my Vodafone connects..

But as soon as I take it out again, the phone dies instantly, and will not even try to turn back on if it isn't plugged in.

Can anyone let me know what I have done wrong?

Thanks in advance.