fixing an iPhone 2G (won't boot up, won't boot into recovery)

[PockyWitch]

Hello dear Apple FP Section. A friend of mine had an iPhone 2G which died and I can keep it if I fix it so of course I wanted to try but I am not very successfull.

It won't boot into normal or recovery mode using an USB charger (or not being plugged in), if I use a wallcharger then I can turn it on but it only displays the apple logo for 10 seconds, then shuts down. Recovery works using a wallcharger but of course that's useless.
What also works is DFU Mode BUT no matter what I try I cannot recover. It will either disconnect while "preparing iPhone for recovery" or if it works (rare chance) it will give me an error 1600, even when I ran iREB before.

Is there any chance to save it ?
I think it might be something with the battery, leaving it plugged into the wallcharger right now and going to try charging it for a few hours and see if I can recover it then.

Edit:
I just opened it up and noticed the black battery wire is disconnected. pushed the battery against it so it would make contact and now it boots up just fine.!!