Smallest starting battery?

[JackConnick]

I have a two bank battery system with two Group 27 105ah deep cycle flooded batteries on the house bank and an isolated Group 27 105ah as a reserve "get home". I figured it was nice to have the extra ah. A regular high cranking battery is slightly smaller, but doesn't weigh much less. The batteries are a considerable amount of weight on my Islander 28.

But I hardly ever use the starting battery. And rarely get half way down the house two battery bank.

I was thinking about lightening up the boat by getting rid of the starting battery, or replacing it with a smaller battery, or even a small emergency portable power source.

I'm wondering what others are using for a starting batteries or a "get home" plan. Yes, there are expensive lithium options, etc out there, but not really worth it for a weekend cruiser.

TIA,
Jack

[edwardc]

I have a single large house bank, and a small separate starting battery. Its a Group U1, about 35 Amp-Hours. It has plenty of power to crank the A4, but the truth is that its only there as a backup, as I never run the house bank below 50%, and its still able to crank the A4 at that level.

Unlike a diesel, the A4 has a pretty low cranking current (around 60 amps I believe)

[Dave Neptune]

Jack, personally I'd stick with the 2 house and one start. If you do take one out, take out one of the house so you will still have a "start".

As far as a smaller battery, I have been using a "U-2" lawn tractor battery in my Calibogie for a couple of seasons with no issues. I am starting a 60HP Yamaha and have a couple radios going too. Plenty to crank an A-4. A friend of mine is using one to start a SBC 383 with 11.5:1 compression in a hot rod and it starts just fine.

Dave Neptune

[JackConnick]

What CCA does an A4 require?

I was thinking to remove the starting battery and just use one of these if something goes haywire.

https://smile.amazon.com/dp/B019RY1HMO/ref=dp_prsubs_1

[joe_db]

What CCA does an A4 require?

I was thinking to remove the starting battery and just use one of these if something goes haywire.

https://smile.amazon.com/dp/B019RY1HMO/ref=dp_prsubs_1

An Atomic 4 draws about 120-130 amps starting. I have a U1 size start battery and it is about as small as you can go. These are 200 CCA. I may go bigger when it dies, it is marginal if the engine has been sitting for a week in December. A group 24 is plenty big.

[Sam]

I have recommended this before and will do so again fyi. I have great luck with a bank o just two Optima Blue top D34 dual purpose deep cycle AGM batteries. They are slightly smaller and about 10 - 12 lbs each lighter and easier to handle than conventional flooded batteries. I now have one 4yrs old and the other going on 12 yrs. I periodically use a charger/maintainer in the off season garage storage. They are very expensive retail but about $250 delivered on line but never ran one down or had a problem.

[Al Schober]

My $.02 based on 30 years with an A4.
Never saw the need for hi-tech batteries, always used simple lead acid.
Boat originally had 2 size 27s with an A/B switch. When I needed more house capacity, I added a gp 24 for engine start and made the gp27s a house bank. Worked fine. At one point I tried changing the gp27s to gp31s, but found they were too heavy for me to move.
More details on request.

[Sam]

Well, I can also agree with Al - my first 30 yrs I used 2 bank flooded deep cycles, liked Delco Voyager etc around $120 +. never really had a problem with my boat on mooring can with a good alternator. The Optima AGM's give me more reserve power per "pound or space". Being a little smaller and lighter they are easier for an older guy to handle in tight spaces. They handle vibrations better and supposedly can operate/installed in any position for those who are heeled over a fair amount. Note: I do have an old Delco, about 14yrs old that I use in the off season to power an auto bilge pump. I have a small 4 amp $50 charger/maintainer that I use when the batteries are stored that has an cycling "intermittent " charge that supposedly "desulfites" the battery extending it's life. Can't swear by it but seems to work well.

[capnward]

What works for me is two lead-acid deep cycle size 27s, with the battery switch set to both. The New Mar PT-14 charger is almost always plugged in to shore power, charging both batteries at once. I use both batteries to start the engine, and for everything else, which is only some lights and the bilge pump. I am almost always using shore power for light, heat, vacuum, and computer, and occasional power tools. If I spend a night at anchor I use one battery for house. The New Mar charger is used by commercial fishermen. It cost over $400 but is worth every penny. It runs almost constantly when in a slip, and automatically switches between three phases; bulk, absorption, and float. I have had one for over 20 years and it has always worked perfectly. However, I had to replace the fan in it a few years ago because it was worn out and noisy.