[rokndad]

Yes, the answer is - to - and + to + is in parallel. The voltage stays the same (12v) but the cranking amps are added (250 + 250 = 500 cranking amps). Each Gill G-35 only has 250 CCA's which even when added is marginal for a high compression 427. But they seem to turn mine over pretty well. We'll see after a while. The manufacturer recommends putting it on a battery tender when not in use. I'll have to get one.