dual batteries?

[Zorm]

Not really what you might think.
Got a 71 F250 camper special with the tool box on the side of the bed. I have been thinking about relocating a battery there but hard finding one small enough and enough amps to start the 390.
Well, i picked up a Optima red top 800cca for my jeep at great price and the gentleman has some smaller yellow top Optimas that are 450cca. The yellow top would fit in the tool box on its side, question or thought I have is to wire two of these parallel to get 12 v and 900cca and mount them in the tool box via a slide out tray.
thoughts from the electrical thinkers out there.

[1972hiboy]

My first question is why? my concerns would be this, your using two small batterys that are somewhat under rated for the application and hopfully hooking them together will see you through. you would be relocating the batteries to the storage compartment and moving the batterys further away from the starter solenoid which is the electrical distribution point for the truck. This would mean potential voltage drop now that electrical power is moving through feet of battery cable vs a few inches that it was before. If one of those batterys starts to get weak it just componds these potential concerns. There would be more of a chance of battery cable rub through at points of contact with the frame or body and you loose your tool box. Whats the benefit?