Recently the aux battery on my '87 = Westy Weekender fried (finally the answer to the sulfer smell - No: the kid = didn't stuff an egg salad sandwich into a heater channel). MY = INQUIRY: Must I replace this battery with the factory spec or can I install a spare = 12V battery I salvaged from my '86 Jetta? If these vehicles do not = call for the same size battery do I run a danger in performing this = swap?