starter and house battery – Alternator or Add-a-battery?

Had to use my NOCO jump box too many times last year when the electronics drained my starting battery so I’m adding a house battery to run the electronics. I’d like to top-up the house battery when the outboard is running and the starter is fully charged. I am looking at 2 options: the MinnKota OnBoard Alternator (https://minnkotamotors.johnsonoutdoors.com/battery-chargers/board-alternator?id=13891&jo-page=2) or the Blue Seas Add-A-Battery Kit (https://www.bluesea.com/products/7650/Add-A-Battery_Kit_-_120A). I was searching through the site here and there were some great discussions about both products and it looks like either will do the job. I also have a ‘regular’ onboard charger that I’ll be adding to fully charge the house battery, if the outboard isn’t run enough to fully charge the house battery. I’m curious as to others’ opinions on these products and if there’s a clear ‘go with _______ ‘ argument to be made.

Also, forgot to ask – what size deep cycle? I was thinking of going with an Interstate Group27 size for the house battery.

What outboard do you have? What are you currently running for electronics?

I have a DF150SS Suzuki outboard, on an Alumacraft 185 Competitor Sport. For electronics, I run the livewell aerator, radio, HELIX 9 on the dash, HELIX 7 on the bow. The trolling motor is on it’s own dual-battery system and everything is connected with the Humminbird network. I don’t always run the Helix up front, if I fish from the main deck on the boat. I have a Group 24 marine battery powering everything now but as I said, there’s been a few times when that battery was so drained that it didn’t have enough juice to start the outboard.

Just put a bigger starting battery in. Problem solved.

Replace the group 24 with a 29 or 31 if you have room.

I’m with Rip and Big. Upsize the starting battery to the biggest AGM deep cycle you can fit. It should be able to run it all and have more than enough cranking amps.
Is your current group 24 a marine starting battery or deep cycle? Lead acid or AGM?

I would not suggest a deep cycle. I would suggest biggest cranking battery that will fit.

Also, do you have a battery cutoff switch installed?

Electronic brainboxes on many devices are active even with the device powered off. I’ve seen it several times where guys thought the starting battery was “bad” because it went dead very quickly after arriving at the lake.

Testing the battery load, I could clearly see that even starting with a fully charged battery, there was enough of a load on the battery from all the little brain boxes spinning away in the background that the battery was losing 3-5% of its charge every day. So the boat owner was starting out a half-charged battery or less to begin with.

So yes, a bigger battery may be the answer, but also I’d seriously suggest looking at a cutoff switch for the starter battery.

Good call Grouse.

TheFamousGrouse wrote:

Also, do you have a battery cutoff switch installed?

Electronic brainboxes on many devices are active even with the device powered off…

Testing the battery load, I could clearly see that even starting with a fully charged battery, there was enough of a load on the battery from all the little brain boxes spinning away in the background that the battery was losing 3-5% of its charge every day. So the boat owner was starting out a half-charged battery or less to begin with.

So yes, a bigger battery may be the answer, but also I’d seriously suggest looking at a cutoff switch for the starter battery.

Yes, for sure – this is one of the main reasons I’m looking to add a second house battery – to keep the starting battery isolated from all those small drains of current. From what I’ve found, either option I posed above (Minnkota Onboard Alternator or the Blue Seas Add-a-Battery) will essentially isolate the starter battery from any drain outside of the outboard. The Blue Seas allows you to select to cut off connections from both batteries so that’s a plus for that system. With the Minnkota system, if the outboard itself had a small draw on the battery when not running, that would still drain the starter battery but nothing in the boat would be drawing any current from the starter battery, even if the Master Power and Auxiliary switches were left on (and I always put both those switches to the off position when done for the day).

I run 3 Helix 12s Gen 3s and Mega 360 plus everything else on a group 31 dual purpose and not one issue with power even on long days. When this battery gets to be year four I start to notice slower cranking, and time to replace. I get them from Menards $129 they are made by Exide its all I run now.

Just run one 29 or 31 series AGM. All you will ever need for what you have.

You have a Humminbird.
Set the minimum voltage alarm at 11.5 volts
or whatever your motor manufacturer recommends.

I run a 27 and am going to jump to a 31. This weekend on the river running 2 12s my battery alarm was going off. I’m glad this came up