I recently modified my battery box to accept the larger size (200 amp hour) Interestate Marine Deep Cycle battery (about $140) including the box. I do not have a charging system on my 6 HP Johnson (1973) OB. So far, So good - Even with about 10 Hrs. on the auto pilot, radio, Depth and Speed... I will be applying a battery charge indicator this weekend. Charging from home dock when needed.
That's got to be a heavy battery. What's it weigh? A battery that size should work for you with no problem.
I try to keep my power consumption to a minimum.
My autopilot really doesn't use a lot of power and I only use my radio when I want to get in touch with the bridge tender on the river.
I removed my cabin dome lights and installed battery operated LED lights in their place. At night I'll light one of two scented candles when I'm in a protected cove on the hook.
A few years ago I replaced my outboard charging wire with a #10 copper stranded duplex marine cable. I have it running through an existing outlet hole in the inside transom, to a terminal connector mounted on the inside bulkhead under the lazarett cover. I don't like those cheap, made in China marine electric outlets and plugs that they sell at Worst Marine. They're OK for plugging in a VHF radio but not for putting power into a house battery. The termination board is far more superior to a cheap marine electric outlet with tiny screw terminals. The term board is as good as going direct to the battery, I think.
