RED wire goes on +, and the black wire gets wired to the body of the car. Which is ground -
Usually a car battery, but it also depends on the size of the battery.
check and clean the battery terminals
NO! where does the power (voltage and current) come from if the battery is flat/dead?
You don't. There isn't any cord that you use to hook up to the computer.
take the battery terminals off and wire brush then and the terminals on the battery too to clean them and then re-hook.
Rubber cord used to hook up light fixtures
you could have a bad ground wire that was my problem
NO!!!!!! You'll blow the battery up. That is a very dangerous idea.The current of a battery and the current from an electrical socket from your home is entirely different and are not interchangeable without a converter. It would be very dangerous to try to hook up a vehicle battery to any electrical outlet without the proper converter, such as a battery charger that is designed to convert the currents.A DIFFERING OPINIONIn theory if you used another battery and two cords this might be possible, The problem is the extension cord will not carry enough power safely. It will quite possibly turn red hot and catch fire.
usb cord
hook a battery to it
Get a charged 12 volt battery hook 12 volt constant/RED to the + on the battery then ground - it should power up.
To recharge a battery you put the solar panel in the light and hook the red cable on the positive and the black on the negative