Offshoreonly.com - Batteries, isolators, inverters, etc...

This may get a bit long - but I need some assistance with an electrical issue in the NorTech. The boat had A/C added to it. It uses an 12v/110v inverter to power the unit. OK - So other than the inverter probably being a POS - I have an interesting scenario on how they hooked up the batteries. What you have are two 31 series batteries in the back of the hull to power the A/C inverter. You also have two battery isolators for each motor. The isolators feed the cranking battery and one A/C inverter battery respectively. On every other boat I've dealt with in the past, including my cruiser, the alternator output goes to the isolator - then the isolator runs to each battery. Whoever did this didn't disconnect the alternator wire from the 90amp fuse on the starter solenoid - which of course is hooked directly to the cranking battery. They did run a wire from the 90amp fuse to the isolator, then the outputs of the isolator are hooked up to (1) A/C system battery, (1) cranking battery... With this alternator output still hooked directly to the cranking battery via the starter fuse - how would the isolator feed a charge to the A/C battery once is starts to get depleted? My understanding is that the isolator will feed a charge to the battery needing it while not overcharging the good one i.e. cranking battery.

Now - you have this isolator configuration on both motors - but your are using the two 31 series to run the A/C inverter, which are obviously paralleled.

Does this make sense? Shouldn't the alternator output go directly to the isolator? Then the isolator outputs goe to each battery? I'm pretty sure that's the way it should be - so let's just say for a minute I'm right. Now that we have that corrected - does having the two 31's in the back paralled create any issues with having both engines charging them - via the isolator?

Thanks for reading and I hope it makes sense.

Capt Ross