Why doesn't it turn back on?

I had already knew that the battery in my iPhone 4 was bad but just yesterday I went and picked up the replacement battery and I watched a video on here and replaced it myself once I got it done it turned on and worked for a few hours then when it completely died I put it on the charger usually takes a few minutes for it to start back up again well it didn't start back up. Could it be the phone that's messed up?