Dual Battery set ups

[lazyxj]

I carry a portable jumper battery, in the XJ, to take care of dead batteries. It’s a less expensive way of providing the security of a second battery.
It works best for me since there is no room left under the hood for a second battery.
http://tinyurl.com/27ny2l8
I have used it more on other people’s cars than my own; it’s great for making new friends.
If you buy one, get the heaviest one you can find for maximum power output.
The lead-acid battery will hold a charge for a long time. I top it off once every month or so with a couple hours of charging with either the 120-VAC or 12-VDC charger.

My XJ has the biggest AGM battery that will fit the stock battery tray and it takes care of everything, including the winch, without problems.
Upgrading of all the heavy battery and charging wires/cables is a good idea for getting the best out of your electrical system. Make sure to upgrade the fuses and fusible links at the same time. Periodically checking the cables and connections for voltage drop should be part of your periodic maintenance. All connections get coated with dielectric grease to prevent corrosion.

In our motor home I have installed a marine 2-battery switch, the same that would be used in a XJ dual battery setup. A wired it using welding cable, including a new cable running from the switch to the starter.
http://tinyurl.com/27gpegg
The batteries are isolated with a dual-diode isolator.
http://tinyurl.com/26y5z6q
When the battery switch is in the 'both' position, the isolator is jumped, allowing power from either battery to flow to the other.

You can also use a voltage sensitive battery relay.
http://tinyurl.com/25stdxj

Being able to jump a dead starting battery with the twist of a switch is nice.

 

[ert01]

There's a lot of info on dual battery setups over at expeditionportal

If you're running dual batteries, they should both be identical batteries (same age even)....

 

[NEWYXJ]

Mean Green sold a dual setup a few years back, but I don't see it on their site anymore.
This could be because it took cutting, grinding and welding to make it fit.
Mean Green was great about it and sent me a second Optima tie down plate and a spare cone air filter for my trouble.

http://www.hellroaring.com/bic75300.php This company makes a great, compact, solid state Battery Isolator / Combiner. pricey, but I think it was worth the money.

 

[lazyxj]

If you're running dual batteries, they should both be identical batteries (same age even)....

Size and age of batteries is a major concern when differing batteries are used in the same parallel or series wired battery pack. One bad cell can drain the entire battery pack.

Separate batteries (or packs) of differing age and size not a big problem, when charging, as long as both batteries are in good condition (not internally shorted) and they use the same chemistry.
Each battery’s internal resistance (impedance) controls it’s own charge rate and prevents overcharging as long as the charging system is working properly. A battery's internal resistance rises as a battery charges.

Many RVs and boats have different size batteries charging off the same power sources, usually the engine’s alternator, and use diodes or relays to share the common power source.
My motor home’s 12-volt, 440-amp-hour coach battery pack
http://www.flickr.com/photos/lwade/1416466406/in/set-72157602104740457/
and Group-65 engine starting battery are both charged by the engine's alternator, connected through the factory-equipped diode isolator.
My previous motor home had a factory-installed relay doing the same job.