Dual battery switch/ACR?

[CobaltVet]

I have a 2011 A25 with the Off/On/Combine dual battery switch from Blue Sea.

As I understand, this switch is intended to be combined with an ACR or isolation relay. I’m unable to find either component- perhaps someone can point me in the right direction?

I did inquire with a local dealer… they said initially that all cobalts with that switch have an ACR, then they looked it up and verified that the 2011 didn’t have an ACR. They sold me an ACR and recommended installing it for the full function of the dual battery switch. In the interim, they recommended running in the combined position.

It’s hard for me to believe that’s necessary as I believe both batteries are charging from the alternator in the “on” position.

I don’t think I want to install the ACR if I have an isolating relay already installed, correct? Where should I look for an isolation diode or ACR? Anyone else have a factory setup with the off/on/combined switch without the ACR?

[stifflkd]

If you have an ACR it would most likely be behind the white panel that the switch is mounted to. If you do not have one then I would recommend setting the switch to COMBINE when the engine is running and to ON when you are hanging out and drawing from the house battery. And obviously OFF when done for the day. After a few times having to do this you will realize the convenience of the ACR as it automates this process. Just set it to ON and the ACR will charge and isolate as needed. Then you should only set the switch to COMBINE if your starter (engine) battery is dead. This will put the two batteries in parallel and allow you to pull current from the house to get the engine started.

[SAB220]

Ditto. There are simple ACR wiring diagrams on the BS web site - follow the wire. If you bought the boat used then anything can be true.
As stiffflkd said if you do have a ACR its important you know the starter (engine) battery and the house battery. The other thing to check is your bilge pump. Suggest your AUTOMATIC bilge pump works know matter what position the boat switch is in

[CobaltVet]

I prefer the ACR functionality with the Off/On/Combine style switch, and I purchased one from the dealer. I just didn’t want to do any harm in installing it by adding it to a boat that already has one or has an isolating diode somewhere I’m not looking.

Also, I’ve read that both batteries should be matched when using the ACR (i.e. don’t mix and match a starting with a deep cycle)? Any real world experience or advice there? Use a pair of AGM dual purpose batteries? Or it’s OK to use one AGM deep cycle and one AGM starting battery with the ACR?

Thanks again!

[stifflkd]

Follow the wires from your batteries to the switch. An ACR or isolator diode should be connected on the battery side of the switch.

It is also okay to use a cranking battery for the engine and deep cycle for the house as long as they are of the same chemistry. Since you are talking AGM's for both you should be fine. With that said I am seeing alot more of the dual purpose batteries. Not sure if it is a lot of hype but finding it harder to find pure deep cycles.

[SAB220]

Good comments. General purpose [AGM], based on age/warranty, also allows battery rotation from starting to house.

[bruceb58]

This is the ACR you want to buy if you don't already have one.

smile.amazon.com/Blue-Sea-Systems-Automatc-Charging/dp/B000OTIPDQ/ref=sr_1_3?crid=2CW4I26M9NHP0&keywords=blue%2Bsea%2Bacr&qid=1663098296&sprefix=blue%2Bsea%2Bacr%2Caps%2C137&sr=8-3&th=1

[bruceb58]

Follow the wires from your batteries to the switch. An ACR or isolator diode should be connected on the battery side of the switch.

It is also okay to use a cranking battery for the engine and deep cycle for the house as long as they are of the same chemistry. Since you are talking AGM's for both you should be fine. With that said I am seeing alot more of the dual purpose batteries. Not sure if it is a lot of hype but finding it harder to find pure deep cycles.

Actually very easy...just not going to find it at Costco or Sam's. Trojan, among others, has true 12V deep cycle batteries made for golf carts. You won't be able to start your engine from one though.

[Titaniumboy]

Bruce,

What is the reason you wouldn’t be able to start your engine?

[bruceb58]

Bruce,

What is the reason you wouldn’t be able to start your engine?

True deep cycle batteries have very large thick plates. A starting battery has more very thin plates. The difference is the surface area that is able to produce the chemical reaction that delivers a lot of current very fast. That is why TRUE deep cycle batteries can't deliver a lot of current and true deep cycle batteries don't even have a cold cranking spec.

With a modern EFI engine, the engine may crank but the voltage drop would be so much that the voltage would not be high enough to reliably run the fuel injection and ignition during start. That's why modern EFI engines require a minimum cold or marine cranking amp spec.

[Titaniumboy]

I have two pair of marine deep cycle batteries that I swap in and out of the boat. One pair is from 2014 and are Kirkland branded from Costco. The other pair are Interstates from 2017. Interestingly, the Kirklands are markedly heavier than the Interstates.

They have lived through stuff that straight up would have killed starting batteries, stuff like letting them go dead over 9 or 11 months of non-use. I have been able to resuscitate them from dead several times. I do wish they had more than 550 CCA for my 496, though.

[bruceb58]

I have two pair of marine deep cycle batteries that I swap in and out of the boat. One pair is from 2014 and are Kirkland branded from Costco. The other pair are Interstates from 2017. Interestingly, the Kirklands are markedly heavier than the Interstates.

They have lived through stuff that straight up would have killed starting batteries, stuff like letting them go dead over 9 or 11 months of non-use. I have been able to resuscitate them from dead several times. I do wish they had more than 550 CCA for my 496, though.

A marine deep cycle battery is not a true deep cycle battery...it's a hybrid battery. Interstate made the batteries for Costco.

It also falls WAY short of what mercruiser specs for a modern EFI system.

If you want to go dual purpose, the DEKA AGMs will do 800 CCA. They sell a version of it at SAMs.That's what I use.

Mercruiser battery.JPG

[Big Block Power]

I have two pair of marine deep cycle batteries that I swap in and out of the boat. One pair is from 2014 and are Kirkland branded from Costco. The other pair are Interstates from 2017. Interestingly, the Kirklands are markedly heavier than the Interstates.

They have lived through stuff that straight up would have killed starting batteries, stuff like letting them go dead over 9 or 11 months of non-use. I have been able to resuscitate them from dead several times. I do wish they had more than 550 CCA for my 496, though.

A marine deep cycle battery is not a true deep cycle battery...it's a hybrid battery. Interstate made the batteries for Costco.

It also falls WAY short of what mercruiser specs for a modern EFI system.

If you want to go dual purpose, the DEKA AGMs will do 800 CCA. They sell a version of it at SAMs.That's what I use.

Mercruiser battery.JPG

And that's for a 4.5L

[Titaniumboy]

A marine deep cycle battery is not a true deep cycle battery...it's a hybrid battery. Interstate made the batteries for Costco.

It also falls WAY short of what mercruiser specs for a modern EFI system.

If you want to go dual purpose, the DEKA AGMs will do 800 CCA. They sell a version of it at SAMs.That's what I use.

Is this the one? $214.32 at the only Sam’s Club in the Bay Area, and is showing out of stock. I wonder if Sam’s Club will accept my Costco membership card?

This Group 31 battery is markedly larger than the Group 34’s that I’ve been running. I would need to upgrade my two battery trays.

https://www.samsclub.com/p/duracell-agm ... _product_9

F3758FE5-D873-4CC4-AF35-CE08C62F962E.jpeg

Here is the Duracell Marine/RV AGM brochure from East Penn Manufacturing (who also make the Deka branded batteries). The part numbers differ from the Sam’s Club part number, but I’m assuming that Sam’s Club received unique part numbers from East Penn?

2152.pdf

[SAB220]

do you have to upgrade the charging system for the full benefit? Double serpentine belts/pulley alternator.