93' Grand Cherokee loosing power

First off, i virtually know nothing about cars so, I'd sincerely appreciate any help anyone offers...

Well, it seemed fine, then outta the blue it wouldn't start...i kept turning the ignition untill it did finnally start... but after a minute it would die. This goes on and on. The battery is obviously completly not dead... So what do you all think it is?

I was hoping it WAS the battery, and all i would have to do is replace it. I really can't afford much else... The battery is not too old, had it replaced maybe a couple of years ago. I havn't tried charging it yet...

Thanks for listening.