I have a 1998 Ford Club Wagon - it has an auxiliary battery located under the van mounted to the frame - I need to get a new main battery - do I also have to get a new auxiliary battery too? - what is the purpose of this auxiliary battery anyway - is it just used to supply a trailer load - does it help start the van? - sure would appreciate any information about this extra battery - thanks in advance - Joe

 

You should always replace batteries in pairs...Is it a Diesel ? If not just get it Load tested just in case....

 

i don't know how its wired, as it was likely aftermarket. if its installed with a multi-battery isolater, then it was probably intended for running accessoreis (RV stuff, etc), or if its wired directly with the main battery, its involved in starting.