??? for the wiring GURU'S!!!!!

I have been thinking about a dual battery set up for my rig now that I'm putting a winch on it, but space under the hood is at premium. So I was on the web today and found some OPTIMA red top 6 volt starting batteries that measured approx. 4"W x 10"L x 8"H and I got to thinking. Has anyone else thought of wiring two of these 6 volt batteries in series essentially making them one 12 volt battery to conserve space. Then running them through an battery isolator along with my other OPTIMA red top so that there isn't any uncontrolled current flow and they all get the charge that they need from the alternator without pulling from the other battery draining both of them. I think could find room for these easier than one fullsize battery. Any input or suggestions, and of course if somebody else has done it already pictures would be fantastic.

Carman

Theoretically possible, but I'd be a bit wary of that - you lose one cell in a battery less often than you lose one battery of a series set.

Odyssey makes some rather small batteries that are 12VDC, and the power density is phenomenal. Perhaps that would be a better option for you?

Also, consider something like the battery setup used for Diesel XJs - use an "air kit" to eliminate the airbox, and the second battery goes there.

Why for do you want an additional battery? Knowing more would allow you to get more effective suggestions - there's nothing stopping you, for instance, from mounting an AGM (Optima) or gel cell (Odyssey) battery in the rear cargo area, for instance. Why you want the second battery and what you're going to use it for are huge factors in deciding the rest...

As far as the isolator idea, use a 100% duty cycle solenoid. They're cheaper, more reliable, and have higher current ratings (I can find 100% solenoids up to ~300A - most solid-state isolators seem to top out around 60-70A, or thereabouts.) You also have the ability to wire up a "two-way bypass" using a solenoid - if your second battery is nearly flat, you can cut it out of the circuit with a switch. If your starting battery is nearly flat, you can cut the second battery in by flipping another switch. Easy.

If you want help with the wiring, let me know. I can gin up custom wiring just as easily as OEM replacements.

Two six volt batteries in series is better than two twelve volt batteries in parallel with isolation between the auxiliary pair and your starting battery. What you propose is very common for motor homes. An pair of twelve volt batteries in parallel are continuously trying to equalize each other and should be of equal age to minimize this.

Check the marine websites for isolators and switches. I thought abought putting a large 12V motercycle gell battery under the hood for a back-up.I put one on my 17HP snowblower and it works great so I bet somthing like that would easily jump a run down jeep battery. Advanced auto sells them but you have to ask because they keep the gell Harly Davidson batteries in back. For what it's worth I have a yellow top optima and it seems to run down as fast as a regular battery when I leave the doors open so a back-up is on the list.

I guess it would work but it would be expensive. They charge nearly the same for one 6 volt red top as they do for one 12 volt red top. And if you have seen them they are literally 1/2 of a 12v red top. IMO what your thinking would work but it would cost twice as much.

If you're "ganging" batteries without an isolator, you'll need to get them as a set, and all at once.

However, since you're running an isolator, the age is a little less important (since the two batteries will be electrically separated when they're not being charged.) This simplifies logistics considerably.

You may want to reconsider using a Red Top tho - a Red is designed to be a starting battery, supplying large amounts of current for short times. This is why I'd asked why you wanted the extra battery - a Red Top may not be for you. If you're running accessories off of it, and doing so without the vehicle running, then you want a deep cycle battery - which is designed for that sort of thing. The accessories are wired directly to the deep cycle, the deep cycle is isolated from the rest of the system when the vehicle is off (thanks to the solenoid,) and you can run them to your heart's content and know you'll still be able to drive home, because your starting battery is still fully charged.

If you're not sure what you want to do, then take a few minutes to plan it. If you can't explain it to someone else, it doesn't make sense to you. If you can explain it to someone else, it gets easier to get help doing it - by several orders of magnitude...