new battery, turns on, says its fully charged and then dies unplugged

So I just got a new battery and soldered it in and finished installing, it booted up just fine, but shows a full battery, but then I unplug it and it dies? Even letting it charge for a while does nothing, did I install this wrong or mess up my solder points, or is it different hardware dying out?

I need some help with this, im feeling pretty bummed out after I felt the install was so perfect.

I resoldered it and fixed the problem, now it works and plays music, I lost my hold button in the process ( wire snapped) so I did what I could and removed the whole wire and works still. Now the problem is, it restarts itself at random and will just loop the Apple logo startup screen, after holding menu and middle button a few times it will start back up only later to do the same thing? Any ideas?