Redundancy..

More's Theory:
If ONE is sufficient,
Then MORE is better.

I have 3 batteries in my truck, the #1 Main battery is in the stock location, #2 Axillary battery in on a bracket I welded that sits on the passenger side fender near the turbo, while the #3 final set of batteries are in the bed of the truck behind the drivers side inner fender, #3 used to be an 8-D Deep Cycle diesel battery but in-place of that I am now using 3 AGM computer backup batteries wired in parallel as one pack.

Axillary #2 Battery is interconnected to the #1 Main battery using #2 welding cable with crimped on brass terminals through #1 Sure Power 1314 Separator then connected to the positive terminal on the #1 Main battery while #3 battery pack is connected from the bed using 00 welding cable along the frame rail where it is connected by #2 Sure Power 1314 Separator through a cable also the the #1 Main battery terminal.

All of my batteries are being well fed numerous amps by my 110-555JHO triple nickle 160-amp high output alternator carried through #2 welding cable and is connected directly to the Main battery positive terminal through a 200-amp T fuse to protect the alternator against a catastrophic short circuit.

https://www.dieseltruckresource.com/...s-t247286.html

There are the separators I am using.
http://www.ase-supply.com/Sure_Power...p-1314-200.htm

http://www.smithae.com/products/sure...eparators.html

Why you ask?
I like lots of redundant power..

My work puts my truck in some dangerous situations, during the daytime hours I will usually have my emergency flashers going all day and then as the night comes all of the marker lights will come on, routinely lights will be on from maybe 4:00 P.M. until 3:00A.M., in the cab I have the usual high output sound system, CD/DVD player, axillary monitors, 1,000,000 CP Collins spotlight, 50-watt halogen map light.

In the Leer camper I have my 3000-watt Sine Wave inverter that under full load will consume more than 300-amps, high frequency fluorescent ballast for my 4' tube fixture, 2) 100-watt work lights, ventilating blower, Viair 380-C 200-PSI air compressor and many things I have missed, just today I was repairing a fence using my 12-amp Skill Saw and 1/2" Makita drill plugged into my inverter all far from any AC outlet.

There have been times I had my 3" submersible pump running off my truck power for hours while draining an underground parking.

Several years ago we completely painted the inside of my son and daughter-in-laws 4 bedroom 2 story house throughout the night with no electricity, all of the lights were plugged into my inverter, I idled the engine for about 10 minuets every hour to keep the batteries up.

I have reconnected most of my loads onto a switch so I can select Main or Axillary battery, basically the only thing my Main battery has to do is start the truck.

There were times that I had left my headlights on because I was using them to light the area, even though the lights are still bright, when you try to crank over the starter it will not turn, nothing like the dreaded click, click click at 3:00 A.M. when you are 50 miles from home.

All I have to do is simply press in on one or two buttons and I can interconnect any battery in any combination together and start the truck for a combination of about 4000-cranking amperes.

If I am running heavy loads I will idle my engine to keep all of them charged,
the 110-555JHO alternator produces 100-amps at a fast idle.

Even though I have a backup generator at home, 3 of them actually, I have plugged in an extension cord from the truck and run it into the house for lighting when the electricity was out.

My truck always starts on the first bump no matter how I drain the battery.

This is why I have more that 1 battery in my truck.

I know this sounds a bit complicated, but it is simple in my head.

Jim