It could still be done, but the 4d is still a heavy battery. Maybe a crank system l8ke they use for spare tires

 

Good point. Might be hard to ratchet up a 4D. But a crack drive could be a clever solution. I haven't mig welded in a dozen years. Might be time to find a used welder and finish my brush guards, build a 4D crank drop-down, and start fitting piping for my innercooler....

 

If I see Flux core wire don't let moisture get to it. I got 1/2 a small spool that I got b to replace

 

Change the cables so only one battery connects to the positive circuit and only the second battery connects the ground circuit. Most vehicles can be done by switching one cable to complete this upgrade. The original design does not allow even usage of both batteries. batteries need to discharge and charge to keep their power. You will find a big difference in cold weather starting too.

 

skimmed the first page and skipped to the end. I have had a group 31 in mine for 4 years now and no issues. Cranks over good and will crank forever. You just have to flatten out one end of the battery tray to make it fit. That said, i do not have a glow plug system on said vehicle, i use an ether injector, so there isnt any load before cranking. I think the reason they have two, is if you get really technical, you theoretically should never discharge a battery beyond 80% or the life of the battery will drop signifigantly, the engineers might have decided that the glow then cranking is enough to drop a single battery below what is acceptable. That said, i have abused my 31 many times, and have had a few bad alternators from the JY, it has been over charged, undercharged, left dead many times and its still trucking after 4 years. To me if it goes 5 years, ive got my $97 worth. The battery is a Les Schwab XHD 72 month (6 year) battery. When the new engine goes in, its getting glow plugs, and still keeping the single 31.

 

What's that reference from? I'd love to read more of the text, just to be more convinced that it's a good idea.

 

One idea for two batteries:
Get a big 'battery disconnect' switch for the second battery, then install a battery isolator.
Unless things have changed, a 'battery isolator' like this: is basically two big diodes.
You put it between the alternator output and the two batteries. In this case, leg 'one' would go to the main battery, and 'two' would go to your second battery directly.
Make sure that the alternator 'feedback' wire is /after/ the isolator, not before.

Now, you just plain start and run on battery #1. Battery #2 is disconnected with the disconnect, but has a separate charge wire keeping it ready. You can also use this for accessories if you want.
If you ever need to, just connect that disconnect and you can then start off #2(+#1)

If you wanted to be fancy, you could even get something like this:
PERKO Inc. - Catalog - Battery Switches - Heavy Duty Battery Selector Switch with Alternator Field Disconnect [8603]
Hook that in between the main battery + wires, and now you can start off either battery or both if needed. Or switch to 'off' and prevent drains if you are letting it sit for a while.

I've used the battery isolator setup for keeping a decent battery bank(4 "group 31" sized AGM batteries) charged in my camper - as the alternator is mostly a 'constant voltage' source, both battery banks end up charged just fine, and neither will 'discharge' the other.

 

The switch and isolator are great ideas.

 

They are used in diesel pusher motorhomes and boats. Any rv shop or boats supply should have them

 

I have had my Interstate Batteries last 10 years per set. Maintenance ( low amp, overnight) charge every six months or so. Unless you run 3 or 4 hours at a time from time to time. Keep all connections clean, and the correct SG for your electrolyte. Alt output at around 13 volts, and you should be ok. You will need dual batteries IF it ever gets really COLD, or you REALLY run it out of "gas" ( Diesel )!!

 

That's the thing. I drive this van on major roadtrips where I drive it for over 12 and 24 hours straight sometimes. I keep the connections super clean with dipole grease, and my Auber voltmeter shows that it always has at least 13.5 and sometimes 14v when driving with my spiffy new 3G alternator. Also, I have a 130Watt solar panel array on the top of the van that has a charge controller to keep the batteries topped up at 14.2V and they are controlled with a NC relay from the "key on" situation, so that they don't contribute to the circuit once the engine is on.

So for all purposes, these Batteries should be living the good life. But if one goes to hell, you have no way of telling because the other "covers" for it. The only way you find out is when the cranking gets hard or something goes haywire, and by that time you are on a job or out on a trip somewhere and you are SOL.

 

Maybe your tryin' too hard!
I agree with you on this, it sucks when you finally do figure it out, and have to spring for a pair, when in theory only one is "bad".