Roger,
I believe any 12v battery that will fit in the box will work.
However:
Starter batteries are not designed to be used as auxillary batteries. Starter batteries are designed for short bursts of high amps. Continuous draw down of a starter battery will greatly reduce its life span. Deep Cycle Marine batteries are designed to be drawn down low hundreds of times without harming them. The Optima sealed marine deep cycle seems to be the best and the largest that will fit (barely) into the hole under the driver's seat (See vanagon.com for details of fitting it). Finally, breathing sulfuric acid (and other gases that come out of a battery) is harmful to your health. The auxiliary battery compartment is not sealed or vented like the starter battery compartment is (or is supposed to be). A sealed battery protects you and your family's health.
Good Luck,
Bill
90 Westy Syncro
    -----Original Message-----
    From: Jen & Rog Johnson <rojen@CAPITAL.NET>
    To: vanagon@GERRY.VANAGON.COM <vanagon@GERRY.VANAGON.COM>
    Date: Saturday, January 23, 1999 12:34 PM
    Subject: Aux Battery 87 Westy
    
    
    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?
     
    Roger
    87 Weekender
    66 Type I
    86 Jetta battery

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