Need second battery pointers

[SSTKO81]

I'm installing a second battery ("house battery") in my '81 SeaSprite w/ Mercruiser 140. I'd like to use that second battery to basically run everything but the starter and ignition system. Meaning all pumps, blower, lights, radio, fish finder, ect. I was hoping I could just move the red/purple wire in the harness over to the new battery and that'd be then end of it, but before I go cutting into the wire harness I'd like to pick the brains of those that have done this before. Can anyone give me a couple of pointers or good ideas?

 

[Bt Doctur]

leave the existing alone and simply add a battery switch, isolator or blue sea system for the house
Hacking up a system thats working is never a great isea

 

[Lou C]

On small boats the “house” and engine loads are not wired separate so the easiest thing to do is to use the simple 1,2, 1+2 and off switch. Just alternate use of each battery and never leave it on “both” since one bad battery can kill the good one. The only time you would use both is if both batteries were each discharged enough so that neither one alone will start the boat. I’ve had that set up for 15 years with minimal problems.

 

[dingbat]

If your going as far as to separate the ignition and house loads, you might as well install an ACR while your at it.

My boat came OEM with two batteries but the “house” was simply a backup with a 1/2/Both switch.

It wasn’t until I installed a full complement of electronics on the “house” battery that I realized the need for more storage and a better battery management plan. Flipping to battery 2 when I got an under voltage alarm on the chart plotter wasn’t cutting it.

When I installed the ACR, I switched both batteries to deep cycle for storage capacity. Moved the bilge pumps, lights and main fuse panel to house battery.

Left navigation related components, ie Trim tabs, navigation lights, etc. on the ignition battery then added a second fuse panel to the starting battery to power the primary navigation devices.

No more low voltage alarms and no more switch roulette. Improved battery life from 3 to 10 years by switching to deep cycle batteries and keeping discharge rates at a minimum.

 

[SSTKO81]

On small boats the “house” and engine loads are not wired separate so the easiest thing to do is to use the simple 1,2, 1+2 and off switch. Just alternate use of each battery and never leave it on “both” since one bad battery can kill the good one. The only time you would use both is if both batteries were each discharged enough so that neither one alone will start the boat. I’ve had that set up for 15 years with minimal problems.

I have an isolator that I’ve wired in; and I don’t really want to hack up the factory harness… if it was as simple as moving a terminal or two around I was gonna split it up…. That’s kinda where and why I’m stuck