On Tue, Jul 28, 2015 at 10:38 AM, David C Brown wrote: > Could you minimise the unbalance by switching the load between the two > batteries at a very low frequency, maybe a mHz? > It's a good idea. However, I'd lose the benefit of a common ground, as the new common for 12V power will also be at 12V in respect to chassis ground - when running on the "top" battery. It would be a real issue of labor and safety to lift all the grounds on the powered equipment - especially radios with antennas. The battery imbalance issue is enough for me to either go DC to DC, or as Russell suggested - a roundabout DC to AC to DC, or even putting a 12V alternator on the accessory belt. I found there are battery balancers made too, for this exact scenario, however they cost more than all the other solutions. Thanks for your suggestions. --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .