Battery sizing and load doesn’t make sense

[Elkins45]

I’ve only owned two “real” boats in my life, but both have had their battery wiring done the same way. The trolling motor gets its own battery and then every other electrical draw is hooked to the starting battery. From both a current allocation and safety standpoint that seems wrong to me. The most important uses for a boat battery would seem to me to be starting the engine, bilge pump, and nav lights. And all of those are fed by the same battery, as are courtesy lights, livewell pump, GPS, etc…

In the case of my 16’ G3 the starting battery tray only has room for a group 24. That’s unfortunate because I have a perfectly good spare battery that could drop in there to increase capacity but it’s too big to fit. Is it a common practice to parallel wire a second battery to add a margin of safety? My biggest problem would be figuring out where to put it where it wouldn’t be in the way.

My second concern would be overtaxing the onboard charger since it would now have 2X the burden to recharge. Thoughts?

 

[dingbat]

I’ve only owned two “real” boats in my life, but both have had their battery wiring done the same way. The trolling motor gets its own battery and then every other electrical draw is hooked to the starting battery. From both a current allocation and safety standpoint that seems wrong to me. The most important uses for a boat battery would seem to me to be starting the engine, bilge pump, and nav lights. And all of those are fed by the same battery, as are courtesy lights, livewell pump, GPS, etc…

In the case of my 16’ G3 the starting battery tray only has room for a group 24. That’s unfortunate because I have a perfectly good spare battery that could drop in there to increase capacity but it’s too big to fit. Is it a common practice to parallel wire a second battery to add a margin of safety? My biggest problem would be figuring out where to put it where it wouldn’t be in the way.

Here is a solution to the problem.

Add-A-Battery Kit - 120A - Blue Sea Systems

Simplifies switching and automates charging for a complete two battery bank solution.

www.bluesea.com

My second concern would be overtaxing the onboard charger since it would now have 2X the burden to recharge. Thoughts?

Don't follow you.........
You use 500W out of a single or two batteries paralleled, you still only need to replenish 500W

 

[Scott Danforth]

trolling motors are generally 24, 36, or 48 volt.

the main motor and electrical system is generally 12 volt

if you want to add a battery, do so. if you want to add a second battery, an ACR, and separate the house loads, feel free.

if you add a radio and other electronic suck-holes for electrons. you may want to separate the house loads from the main motor.

is this an outboard, or an I/O?

 

[Elkins45]

Don't follow you.........
You use 500W out of a single or two batteries paralleled, you still only need to replenish 500W

This was my thinking as well, but I wasn’t confident I was correct.

 

[Elkins45]

trolling motors are generally 24, 36, or 48 volt.

the main motor and electrical system is generally 12 volt

if you want to add a battery, do so. if you want to add a second battery, an ACR, and separate the house loads, feel free.

if you add a radio and other electronic suck-holes for electrons. you may want to separate the house loads from the main motor.

is this an outboard, or an I/O?

It’s an outboard, and fortunately one that doesn’t require extended cranking. It’s just that I frequently am away from power for a week or so and I worry about the extra load. The motor doesn’t keep the battery fully topped off because it often takes a while to being it back to full charge when plugged in.

It’s probably just paranoia on my part. I have successfully pull started this outboard in the past when the battery suffered an internal fault and died suddenly. It’s only 50 HP.