Another Dual Battery Post

Been thinking about installing a twin battery system in my little 4.7m Quintrex coast runner with 60HP 4/stroke on the back,  haven’t had a problem to date, but just to be a little more self-reliant when we’re out the back of GI on FFB etc.

The battery in the boat is still fine (can’t see a date) but I don’t know it’s full history as I’ve only owned her for just under a year. I currently take a Lithium jumpstarter battery pack out with us and haven’t had to use in anger but think a more permanent solution would be better peace of mind.

I don’t have an huge loads only the usual electrical for this size craft -  Nav lights, bilge pump, VHF radio, 7” combo fishfinder/GPS, some LED strip under the gunnels, USB charging port and cig lighter socket just in case.

Most operating is daylight hours.

Going to use a Blue Sea Mini Add-A-Battery kit (65A charging) and buy a new battery for starting and move the current battery over to power the house circuits.

Should I just bite the bullet and get two new batteries and be done with it?

Thinking a standard marine battery with at least 70AH would suffice for the above house loads?

I have room next to the existing battery for the second battery or alternately I can put it on the other side of the transom with slightly longer cables to distribute the weight more evenly, thinking opposite side would be best as she’s only little and light?

Currently I have rigged up a weatherproof Anderson socket on top of existing battery box via a flying lead for charging with a smart charger in the shed, as I got sick of trying to remove the lid from the battery box (difficult), will this still work via a VSR for a dual battery setup when isolated from the loads (off) ?

 Thanks in advance guys.



Faulkner Family's picture

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 prob better using your

Tue, 2018-08-14 17:00

 prob better using your current battery as primary until it dies. reason being if you use new one as primary and it gets drained and you switch over to second and find it has shat itself. dont think you need to go 2 new ones, and yes one either side. i know its only battery weight but it can intefere with the way the boat rides if too much weight on one side


RUSS and SANDY. A family that fishes together stays together

Rob H's picture

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 Can't it be pull started in

Tue, 2018-08-14 17:59

 Can't it be pull started in an emergency?

Most outboards of that size can, if so I wouldn't bother, assuming you physically can.

I had a F115, and tried unsuccessfully to pull start.

Of course that was in the backyard with a couple of frothies under the belt but was an interesting excercise


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Everyone's just winging it.


Scotte's picture

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Date Joined: 07/12/06

 I'd just replace the current

Tue, 2018-08-14 18:12

 I'd just replace the current battery if its known to be over 3 yrs old

sea-kem's picture

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Date Joined: 30/11/09

 I guess it depends as well

Tue, 2018-08-14 18:19

 I guess it depends as well on where you go, if anywhere remote absolutely duals. Just gives you peace of mind, I had a battery shit itself on the river once and was good to know I could just switch over and away we went without the hassle of trying to flag someone down. Also good for back up radio power if you do get in the shit.


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squidvicious1's picture

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Date Joined: 22/07/10

 Any battery business can

Tue, 2018-08-14 18:43

 Any battery business can load test it and that will give you how good it is.  

Grumbler's picture

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Date Joined: 31/07/18

I will second Rob H on the

Tue, 2018-08-14 19:08

I will second Rob H on the pull start as an emergency backup.

I had same thoughts when I was building my boat. Initially duplication looked like a good idea. But then I started to think about battery management to keep system operational. There are two ways. Switch batteries manually to keep them charged. The other is to have some device that manages batteries automaticity. First depends on memory and more hassle in general. Second could be quite expensive and not necessary reliable in marine environment.

I have approximately same load as yours and I ended up with one 105 Ah dual purpose (deep cycle/starter) battery. It is an overkill for such load under normal use but I have two quite powerful bilge pumps that I want to be operational as long as possible without motor running. Even with running motor, 10 amp bilge pump eats more juice than 60 hp motor may produce. Yamaha 60 4-stroke has 8 amp available for charging if memory serves me.

Another thing about batteries. Quite often people use them till battery dies instead of replacing them in regular intervals. Again, there are two choices. Replace battery every 3-4 years or have serviceable pull cord and back muscles ready :-)

gruntre69's picture

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Date Joined: 15/10/16

 I agree with Squid, get it

Tue, 2018-08-14 22:35

 I agree with Squid, get it tested. No point chucking a good battery and if you know it's good and have the Lithiom jump pack, you are good to go! Like Rob said, you can probably pull start it, it would be a good thing to try.

I like the Blue Sea stuff. I have one of their high currect VSR units handling the dual batteries in my 4wd... 500A continuous winching current...


 Marine trimmer NOR (available for clears, tops, carpet, upholstery, custom equipment covers)

Posts: 428

Date Joined: 20/02/11

 You could look at running a

Wed, 2018-08-15 07:12

 You could look at running a very good single like the Deka Intimidator 31 (105 Ah) as you already have the charging sorted when not in use.



Deckie's picture

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Wed, 2018-08-15 09:53

I run a single battery but carry, like you, a jump start pack. It is easy to store and can be moved if needed, a handy thing in a smaller boat. I also connect up my C-Tech charger to the battery when it is just sitting there and make sure the night before I head out that the jump pack is charged.
A spare marine battery can be a lil expensive just to have sitting around waiting to be used, especially when it is a just incase unit. Get the one you have checked to make sure it has still got a good cranking output under load. Even new batteries have been known to drop a cell now and then. Good luck...


Cheers & Stay safe

Hose A's picture

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Date Joined: 10/05/16

Thanks for all the feedback

Wed, 2018-08-15 12:33

I think i'll whip the cover off this weekend and have a go a pull starting her up. Having this as a backup to the backup will go a fair way to easing my battery anxiety .

I think I may stay with the single battery for now and definatly get it tested. May upgrade down the road a bit.