Here's a picture of my dual battery set up with two PC1200's in the original tray. 

House battery is on the left with it's pos terminal attached to the house loads (10 ga red wire), winch, and to the combiner relay. 

Starting battery is on the right and it's positive cable goes to the "Priority Start" module.  This is an electromechancial device (sounds like it actually has a little motor in it) that monitors battry voltage and disconnects the load from the positive battery terminal if the voltage goes below that required to start the car.  From the priority start, the cables go to the starter and to the combiner relay. 

That's the combiner relay on the left between the house battery and the air cleaner.  It's good for 300A continuous and something like 1000 amps for short periods.  The red lever on the right side of the relay lets you manually combine or manually disconnect the two batteries as well as leave it in "auto" mode where the batteries combine when the relay sees 13.8 volts and disconnect below that (with some builtin time delay so they don't disconnect every time the alternator ourput drops when you're idling).  The relay also has a line to allow the switching to be done remotely, but I don't have that feature hooked up yet. 

The bateries are clamped down by home-made brackets that engage the G's original battery hold down features and clamp the Odysey's by their lifting handles.  Works pretty well.  They're steel lined with rubber and painted black.

Grounding cables combine both batteries and then connect to the lighting relays on the left and the engine head on the right.  From teh head another cable runs down to the body ground beneath the battery tray, then on down to the chassis and starter in factory fashion.  Going through the grounding really cleared up som annoying problems I'd had where my fuel and temp gauges would jump to the beat of the music when I had the stereo turned up.  I think that was due to bad connection at that body ground point beneath the battery tray.  All better now.

 -Dave G.

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I bought the stuff separately. Batteries from my local Batteries Plus store, Priority Start from BatteryStuff.com and the BEP 300A VSR from Boater's World. The setup is pretty clean. The cables could be higher quality. Updates never end, you know.

The only slight downside is the battery rating. I think these little buggers are only something like 44 Ah each. With the Priority Start module in there watching out for your ability to start, a really good argument could be made for a single monster battery. Run it down all you want and let the Priority Start watch out for your ability to start the engine. It would be a good bit simpler than my current set-up.

 AMZ's point about potential to fry batteries is a good one. Right now I'm a little more suceptible than I'd like to be. The trouble with the current setup is that the alternator is connected to the starter so it senses voltage there.  Bad connections and such cause the batteries to be actually GETTING a different voltage than the alternator is sensing.  I only know enough about this subject to be a little uncomfortable.  I have to do more research to figure out what's teh best way to connect the charge lines and sensing for the alternator to be the most robust.

And yes, volt meters are going in with the gauge package that goes with the 617A.  The top of my dash will look like a cockpit.  Volt meters, water temp, oil pressure, oil temp, boost, and exhaust temp.

-Dave G.

PS - thanks Dai for suggesting it might be a kit.  When I was fabbing stuff for my racing buddies they used to tell me the best compliment you could get was when someone asked where you bought the component.;)

Just for reference, one thing to note in all this has come up in recent pix. 

The battery tray on RHD diesels is SIGNIFICANTLY differently shaped than on LHD petrol trucks.  I'm not sure if the tray shape goes with the steering config, or the motor, but I'm pretty sure it's the former (steering).  The only ones I've had in my posession turned out to be LHD petrol and RHD diesel but for instance the particular battery pictured in Kermit's post won't fit in the tray of a LHD (petrol at least) truck.

That looks like one wicked-powerful battery though!

 -Dave G.

Still workin' on it!

I've got the manual trans flywheel out being match-balanced to the flywheel that came off the motor.  I also need to order a couple more parts from Sean (clutch).  But once I get those two things squared away I should be ready to go.  I basically stuck, "Part-out spare G-wagen" into the middle of the project as a way to obtain the flywheel. :(   So that's what I've been working at since last November.....Yeah, I'm slow....

Should be ready to make the conversion in a few weeks though.  I really want to get it done before I have to go back to driving it full time.  The 40 mpg motorcycle is really spoiling my wallet.  Going back to a 17mpg G would be better than a 12 mpg one. 

 -Dave G.