Sounds dicey to me. If one develops a problem, the other would be at a different potential, even with the key off. They do have hydrogen in them, you know. Think Hindenburg.

 

The real question is why do you think or want dual batteries?

 

Exactly. Try a new Everstart from Walmart set you back about a bill. 3 year guarantee 100% replacement even without the receipt I just bought one liked it so much had my son buy one for his when it went south. No problems whatsoever.

 

I don't see the issue, that is how you are supposed to hook up dual batteries, I would also run a ground from the second battery to a good connection on the body.

 

That is not how you do it. You at least need a battery isolator to ensure you don't do damage to one or the other batters.

 

While it is interesting, and without touting my electrical background, I see more problems that require really good solutions and careful monitoring, than I do benefits. Benefits, you could argue reserve cranking amps, but, it it's -30C outside neither battery will be charged anyhow.
On the problem side, as I already said, for one, if one battery is flat and the other charged, without a complex isolator, the charged battery could offer more charging amps than the flat battery could take safely and render it damaged or worse, it might ignite it. All it would take is a flaky connection somewhere, and any battery with a lead post is going to have that connection loosen over time as the soft lead collapses. This same problem occurs with aluminium house wiring which was banned, connections loosen up as the aluminium is soft. Not to mention any other connection in your system of parallel batteries. Not to mention any differences at all between the batteries such as age, ..anything that could cause a voltage difference. If it was such a good idea they would have built it that way to start with imo. In farm or construction equipment this might not be such a big deal, maybe they do it there? my two cent

 

 

My F250 7.3 has two batteries and no isolator, it came from the factory that way, along with every other Diesel pickup I have worked on.

 

Yes and it works because the batters are identical. The second you need to change a battery and its different you can run into issues which is what the isolator helps with.

 

Nope.

I've run two different batteries in my DMAX before. No problem. It also doesn't have any kind of isolator. If they are both 12v, your charging system would not be effected by dissimilar batteries. It's not ideal to continue to run a dual system if you know one is on the way out though. It will continually drain the good battery when the engine is off.

The only time I've run any kind of isolator was if the charging system wasn't able to keep up with the electrical demands. In my old Rhino I had a bunch of lights and a big stereo. The OE charging system couldn't run all of it, so I installed a second battery for all the lights and stereo. Then used solid state isolator to monitor voltage on both batteries. If the primary (starting) battery was good, it would parallel the batteries. It would also parallel the batteries when cranking if the second battery was charged.

 

There is no problem. It is an industry standard that is done all the time on motor homes, semi trucks and as mentioned some diesel pickup trucks. If you do it, don't forget to upgrade your cables to handle that much current

 

 

The cables from the last battery in the chain to whatever you are running. Starter yes, but particularly something like a Warn winch which can pull as much as 800 amps if it gets pulled down far enough