Electrical problem?

Got an old Lebaron, not sure of the year :uhoh: sorry its somewhere between 88-93, its old. Well the battery is dead, so I plugged in my battery pack and started it up it runs fine. However unplugging the power causes the engine to just shut down. So obviously an electrical problem. I don't want to put a new batt in or i'm sure it will just drain it. I am here to ask you experts, what to check. Any help would be great I am trying to get this running so my friend will have a car.

The battery just provides a jumpstart for your car...the alternator keeps it running. If your car doesn't stay running when the power source is removed.....you more than likely have a bad alternator. You can either have it tested or just replace it.