I'm fully in the grip of winter up here so contemplating spring projects.I have a truck camper with a battery box that only allows for 2 grp 27 batteries which I have installed now (2 x 12v)I would like to add some more battery capacity, probably by mounting the batteries in the truck in front of the wheel well before I load. For these batteries I was thinking of going with dual 6v's probable Trojan t105-re's.Electrically I guess I could combine them by wiring the 6v's in series and then in parallel with the others but I think this is a bad idea.So is the only solution to separate the banks with a 2-bank switch or is there more of an automated solution to be able to use the capacity of all together and keep them all charged.

Bad idea, different charge/discharge parameters. Go with 2 more GP 27's then hook them all together.

With mine there is room for two end to end up front each side, and the camper slides right in past them. That would make six batteries possible but I have only done it with one truck set on the driver's side.I wire up the two truck bed batteries (series if 6s, parallel if 12s) and use jumper cables to parallel that set with the set inside the camper. My camper set is inside up front down low (no access to outside) so I cut a hole on the left front down there and installed a plastic "cable hatch" that allows me to pass the paralleling wires from the inside set to the outside set which is real close out there.I have the wires dangling outside when sliding the camper in, and when the camper is part way in so I can still get at the truck bed set and the wires now reach, I make the connections and then slide her in the rest of the way.If your camper batts are accessible from outside you can just use a set of jumper cables. Clamp to the truck bed set with the wires down the outside of the truck, slide in the camper, tuck the wires in where you can get at them later, arrive at the campsite, open your camper battery door, and clamp on.I have no problem with paralleling a set of 6s with a set of 12s when it is just while camping. At home charge them up to full separately according to their own battery specifications, and then Float them. Don't leave the different kinds of batts in parallel with no float charger on them except for when actually camping.

batteries do not like different battery types or sizesand not to crazy about different ages of batteries.

Hedge, You actually got very similar answers from both BFL and Chuck. The executive summary could be: Lead/Acid batteries do not play nicely in parallel and the more different the less nice-nice..... I will bet you dollars to donuts that one of your current 27s is weak. (Hint, this is a sucker bet that I already won because you have used them and parallel jars will never equalize while strapped together.) Now, when you mix that with the T105s of any golf cart batteries that are true deep cycle/ BFL has a good plan, and it will work, but it is a recipe for excitement because you would now have 3 different batteries in parallel in your case. To survive this, you need to do three things. Put in the switch so your separate (3) banks can be charged to full density individually, Separate all three banks with some gunga-mama fuses (like make charge rate *1.5). And the last is tough.... THINK. You can discharge all three banks in parallel for short bursts. But, do not leave them that way for longer than you must. Oh, I almost forgot, carry baking soda to clean up the acid spill when one of then (probably a Gr 27) explodes. I did a lot of boat work before the depression. I got to clean up more than a few of these. I always had soda and gloves in my kit. I like doing these job for insurance coverage, it is nasty but it pays good. Matt

You don't need a switch. Before you leave the campsite to go home, you disconnect the jumper cables. After you get home, the camper is slid off the truck, the stands go under it, and the truck bed battery set goes into the garage to be recharged and then maintained on a Float there (with a battery charger for that) until the next camping trip. Now you have your truck back for other jobs.The camper battery set gets recharged in place and then left on the camper's converter to Float with shore power from the stick house.

Adding more batteries | Good Sam Community

22 Replies

BFL13
Explorer II
Dec 08, 2016
With mine there is room for two end to end up front each side, and the camper slides right in past them. That would make six batteries possible but I have only done it with one truck set on the driver's side.

I wire up the two truck bed batteries (series if 6s, parallel if 12s) and use jumper cables to parallel that set with the set inside the camper. My camper set is inside up front down low (no access to outside) so I cut a hole on the left front down there and installed a plastic "cable hatch" that allows me to pass the paralleling wires from the inside set to the outside set which is real close out there.

I have the wires dangling outside when sliding the camper in, and when the camper is part way in so I can still get at the truck bed set and the wires now reach, I make the connections and then slide her in the rest of the way.

If your camper batts are accessible from outside you can just use a set of jumper cables. Clamp to the truck bed set with the wires down the outside of the truck, slide in the camper, tuck the wires in where you can get at them later, arrive at the campsite, open your camper battery door, and clamp on.

I have no problem with paralleling a set of 6s with a set of 12s when it is just while camping. At home charge them up to full separately according to their own battery specifications, and then Float them. Don't leave the different kinds of batts in parallel with no float charger on them except for when actually camping.
Boon_Docker
Explorer III
Dec 08, 2016
Bad idea, different charge/discharge parameters. Go with 2 more GP 27's then hook them all together.

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Adding more batteries

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