You should have a battery disconnect switch for both batteries. Turn it to off position whenever you are charging with NOCO. ACR is for motor charging when running.

 

I do have an isolator switch, suppose I should have mentioned that. That makes sense, it would disconnect the batteries and take the ACR out of the equation.
Thank you!

 

The ACR needs a switch in the ground wire. Otherwise can drain batteries over a couple weeks. Draws 15 milliamperes when not energized. Just turn off the switch and ACR is out of circuit.

 

You want your dual bank charger set up like the ACR doesn't exist.

 

Depends where the ACR is hooked to batteries. Normally Before the disconnect.

 

The dual battery ACR calls for a fused ground connection so you can remove the fuse (if it's in a convenient location) vs having an off/on switch on the ground wire. I have the ACR system on a boat with two batteries and two ACR's on a boat with 3 batteries. The 3 battery boat also has an onboard plug in batt charger connected to the two starting batt's. If I want to charge the 2 start batt's and the group 27 house batt I turn the 3 batt switches so all are connected.

 

You should never charge batteries in parallel if you want them to last. An acr is a fairly dumb device that looks to see if anything is charging your batteries (an alternator or a battery charger) then automatically puts your batteries in parallel. So you want to defeat the acr while charging so it doesn't put your batteries in parallel.

The sure way to do this is to add a switch to the ground wire of the acr. When you install your acr be sure to install a switch and fuse in the ground lead of your acr. Whenever you store your boat or run your charger, you will turn off that switch. As already said, without that switch, or if you forget to turn off that switch, the acr will slowly drain your batteries dead.

This is one of the ironies of installing an acr: people install them to keep their batteries charged, but they instead end up killing off your batteries if you store your boat and forget to turn off the mickey mouse acr ground switch. And then if you forget to turn the switch back on, the acr silently does nothing when running your boat: you get zero feedback that the acr is not working.

A DCDC battery charger is a WAY better choice to keep both batteries charged for a slew of reasons. Keep in mind that when one of your two batteries goes bad with an acr, every time that acr turns on, the good battery drains down IMMEDIATELY towards the level of the bad battery (potentially hundreds of amps current)! So in my mind, you have essentially made your boat LESS reliable by adding an acr.

A simple 1/2/Both battery disconnect switch that you switch from 1 to 2 every other day is more reliable and simpler. If you really want a system that requires no manual intervention to keep both batteries charged, a DCDC charger like the Victron Orion XS in place of an acr is a more modern, reliable approach than using the 1950s technology of an acr that uses brute force to short both batteries together automatically.

 

Follow up, color me stupid but I completely forgot (should have walked the job!) that each battery has an inline breaker between the ACR and the + terminal. Easy Peezy solution to isolate them and use both charging banks. Thanks for the input.