turns over once, wont start sounds dead but wont jump

Ok, so I just got my third XJ ('90 laredo) last week and it has a few problems...
A couple days last week I have gone out to the Jeep to find it completely dead, not any power to even make it click in the engine bay... so I jump it and it'll start fine no problem... well, That happened a couple times.

Now yesterday we started it no problem, went on a couple trails and then stop'd to talk to someone and shut it off. When going to restart the Jeep to leave, it was completely dead... wouldn't do a thing. We got the jumper cables out and tried to jump it, it turns over once and the battery guage on the vehicle jumping us drops way down to 8 volts or below... It draws all the power from the vehicle and only will turn over one rotation.

Anyone have any idea what might be causing this? maybe the starter is bad and draws the power constantly? or it's stuck? I really don't know, any help would be appreciated.

I would start by checking all the wires from the battery-make sure they are not corroded and the grounds are well conected and clean. Have you checked the battery with a multi-meter? You should check it while off and then again after it is running.
Most any auto parts store can check both the alternator and the starter. Also check the fluid level in the battery.

Grounds.

Alternator.

Hold a screwdriver up to the back of the alternator while engine is running, if its magnetized, your alt is good.

well, we connected it to another battery and it does the same thing and just drains it bad.

Test the battery. Sounds like a bad cell.

Oops.... reread that last post. If your original battery was completely out of circuit, never mind.

Check your connections.

well, replaced the starter and it fired right up and ran like a champ about 3-4 volts higher then normal also. My guess is that the inside of the starter was friend and would continually draw power.

thanks for all of those that help'd try and diagnose it.