It all really depends on your end goal. Running to a third battery does allow you to run equipment with the engine off without worrying about draining your starting batteries, which is very important in some situations. In this situation running a second Orion converter to use as the charger for the third battery would be the way to go.
If you are primarily using it while running the engine, then the third battery is unimportant, especially if the radio box has it's own internal battery. Just adding an addition Orion charger either in parallel to the first, or to it's own dedicated Anderson plug is less complicated and cheaper.
I am re-posting my PM to help add to the confusion or help others understand.
Many way to go about it
Your M1123 with a dual output alternator with the 14 volt balancing tap connected correctly and quality batteries is the easiest, most reliable, cost effective. IMO
That alternator with the tap connect is capable of 50 amps. I would not be concerned one bit .. IMO. It will / should handle any Ham, GMRS, CB requiring 12 - 14 volt. These sets on receive / stand-by draw an amp or so... Peanuts.
Now transmitting (and this can vary) will be higher. Say a 50 watt FM transmitter (HAM, GMRS) in the range of 10 to 15 amps and note this is intermittent only when key down. This duty cycle again is peanuts as the battery is doing the work and during receive the alternator is charging.
I see a FT-991 all mode rig and again on receive a couple of amps ... No biggie. On transmit and depending on the mode CW, AM, FM, SSB and again power settings and duty cycle, same story. SSB and CW on the HF bands, wide open, peak power RF output of 100 watts, might see 24 amps and that's on voice peaks / key down, dit's & dah's. So the short / duty cycles of transmitting, instantaneous load on the battery, one would have to talk all day and night with the engine off. LOL
Having a third 12 volt accessories only battery, would / could isolate the vehicle for starting. That could be done with a simple / cost solenoid for isolation to powering just radios / lights... allowing for "get out of dodge" starting. Operation could be under "RUN" or manual switch control / cheap.
I would not go down the rabbit hole or money pit in a design that not needed when having a dual output alternator. All ready have the BIG BUCKS set up.
Some of the voodoo all around 12 volts in HumV's falls to the 60 amp units in old M998's. That was a problem to balance the two batteries when the obvious was to connect to the rear 12 volt battery turned into a balancing act mess. That's where the Orion / converters would be the solution in this case.
Camera's, radios, stereo unless it is a mega 500 + watt mega blaster rockin the neighborhood NO problem IMO.
Lights (don't know what Ya got) but LED's are very low as compared to incandescent so some simple calculations will put you in the ballpark.
Watch out charging the internal radio box battery. Nice set up by the way
. Should have it's own battery regulator (ideal) and follow standard good practice with DC circuits... Fuses, wire gauge, connectors, etc.
Hope this helps.
That's my shocking approach
, CAMO
