I don`t see how a battery that goes dead takes out a ECM? Never happened to me and never been even a concern.
Worry is a misuse of the imagination, if you wanna worry, worry about something that could actually happen.
Thanx. Dan

Making this too difficult.
Use 2nd battery for back up starting only.
Make sure both batteries fully charged before boat hits the water.
The ACR is a good device, not a must, but definitely nice.

Dan,

I’m not so much worried about the battery taking the ECM out. Just the battery that is feeding the ECM going dead and me not having an ECM until I get a new battery. While this system is about as redundant as I’m going to get, I’m still going to be concerned about it until I hasn’t let me down for awhile.

Thanks. Brad.

SB,

Not really. I'm going with it as is. To my knowledge, no such automatic switch is available, so it is what it is. I’m a full advocate of a redundant battery system, and this is something short of truly redundant. I'm just a problem solver, and there is room for improvement here.

And I have to disagree here. The ACR is a must. While addressing of the fragility of the ECM, and maintaining any sort of redundancy in batteries, the ACR isn't a luxury. It's a necessity. Otherwise, you only really have one battery. What good is having a backup battery if there is no ECM to run the engine?

Thanks. Brad.

Guys,

Getting ready to dig into wiring this ACR. Seems pretty straight forward, but...

Instructions suggest 4ga wire and a 100-125A breaker/fuse for each bank. This seems nuts to me, as it's only a 10g wire coming off the alternator. Does this make sense? Or should I have had a larger wire coming off the alternator from the beginning?

Thanks. Brad.

It could at times may be needed for the starter correct? That is where the current draw is, not the charge circuit from the Alternator.

Full disclosure I did not read the spec sheet on it.

Brad , why do you hate instructions so much ???

This is how I did mine because I like to follow manufacturer instructions, figure they probably know best !

Wildman,

No. The two lugs of the ACR are connected to the two battery lugs of the switch and actually disconnects, disengaging the parallel circuit, while discharging (starting or running the stereo while anchored, etc.), so the starting load only goes through the center lug of the switch.

The only thing that makes sense is a scenario where one battery has been significantly depleted and draws heavily on the other battery during charging, when the parallel connection of the ACR is engaged. Outside of that, I can't see the benefit of 4ga wire when it's only a 10ga coming off the alternator. Thoughts?

Thanks. Brad.

Dan,

I'm not hating on the instruction. I will be following them. Just trying to understand the principle.

I see that you only have one breaker in the parallel circuit, when the instruction say to have one on both sides. I guess that makes sense, as the circuit only needs broken once.

Thanks. Brad.

Why make this so difficult? I have ran every boat that I have had with the battery switch in the "both" position and I have never had to be towed in because of dead batteries. I understand that a shorted battery could cause issues with doing this but the chances are small. You are way more likely to be towed in for a broken drive, overheat condition or some other mechanical failure.