Emergency power for nav lights & radio

[john61ct]

OP, a "big picture" design option to consider.

Just keep to two banks. One big House, one smaller Reserve, either whichever chemistry you like.

Major charge sources direct to House, can be switched to Reserve, but usually latter just kept topped up via B2B or echo charger as appropriate.

Two load circuits, Critical and Auxiliary.

Engine, safety including navigation, comms etc, vs non-essentials.

Auxiliary usually switched to House, Critical also, but periodically put on Reserve for test cycling, confirm all working well.

Otherwise Reserve is not usually used.

Yes may require re-wiring, maybe more costly than adding yet another bank but greater KISSimplicity, I think touches all the bases, but of course devil's in the details.

[hellosailor]

Or you can just buy lithium chloride primary cells from companies like SAFT. Available in D cell size, ten year shelf life, same thing that EPIRBs use. Forget about recharging and all the rest. Not cheap, but they don't leak and they would let you use portable nav lights without any fuss.

For that matter, the newer premium alkalines from all of the big three promise more than a ten year shelf life as well. So for emergency backup? No, really, look at self-contained portable lights running on D cells.

[bluewatervet]

So what is your opinion on Optima yellow top batteries, John.

[john61ct]

Good for cranking engines, but none of that brand suitable for House bank deep cycling.

Lifeline, Odyssey and Northstar are the good AGMs if you really need sealed or high CAR, but otherwise old school FLA is best for robust value.