That is if it fits...
hey dude when I meet up with you we can try switching your battery with the one from my car, its dead right now but we can charge it before we put it in, and if it works we can work something out where you can keep both batteries... let me know.
it could be a ground cable somewhere, or the voltage regulator, get your alternator checked, the car should NOT shut off if the battery dies. you should be able to unhook the cables and pull the battery out while the car is running, and it will keep running, if not, its the alternator.
maybe his alternator cant handle the wattage, you CAN run a car without a battery for miles and miles and miles etc. until u shut it off, its there to power the starter and accessories pretty much, but that system is still putting a large load on the alternator.