La_Bolt_Fan
Los Angeles, CA
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Hello all,
I am new to rv'ing, in fact we have only one trip under our belts. And on that trip (4 days) of course my 1 battery died every nightso I recharged the next day. We have learned the way we were using the power was wrong, too many lights, furnace, etc. So I put in a second battery since we will probably never go to places with hookups, we like the privacy of being in the middle of nowhere. So here is what I did, please, you veterans, let me know if you see a problem with his technique:
I installed a battery cut-off in both boxes.
Ran the red cable from the tt to terminal 1 on the cutoff in battery box 1.
Ran a cable from terminal 2 to + on battery 1.
Ran a cable from terminal 1 to the cutoff in battery box 2.
Ran a cable from terminal 2 in battery box 2 to + on battery 2.
Ran the black cable from the tt to - on battery one and from here ran a cable to - on battery 2.
I hope you can follow my details. This way I can turn off both batteries, or use one till it goes low, turn it off and turn on the other one while the first one is turned off. I can charge them separately or together, it just seems to last longer this way instead of just wiring them together.
I would appreciate your thoughts, Thanks!!
Backpacking one week, RV'ing the next!
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rvsatek
AZ, USA
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Joined: 05/23/2004
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I see your reasoning in wanting to use the batteries separtely but it is better for the life of the batteries if they are used as a bank of two. Pos to pos, neg to neg with only one bat. cutoff switch. Otherwise the battery will dishcharge at different rates and the lower charged battery will bring the other battery down to its level. But then again if you NEVER run them as a bank of two it wouldn't hurt anythiing.
Larry
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jauguston
Bellingham, WA
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Larry has it right. Better to parallel the two batteries. The amp-hour capacity of a battery varies with the rate of discharge. The faster you draw power from it the less AH you will get. By paralleling the batteries each will be discharging at half the rate it would be if it was used alone. It is a good idea to monitor your battery bank voltage and try not to discharge below 50% charge (12.2v). That reading would be after the batteries have rested for several hours. You can buy a good digital 0-20v digital volt meter on E-bay for about $10.00 plus shipping that has two digits to the right of the decimal point. I have one mounted in a panel inside my coach where it is easy to see.
Jim
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skipnchar
Topeka Kansas USA
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IF you parallel the two batteries AND they are not matched (same brand - size - and age) the weaker one will draw down the strong one and YOUR method would eliminate that problem. The only down side is that you have to manage your power manually rather than turning it on and forgetting it.
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jauguston
Bellingham, WA
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A VERY unlikely issue. Always possible and that makes it worth posting I suppose like a lot of other very unlikely things that get posted just so the poster can have his say. but I wouldn't lose a lot of sleep that it will happen to you.
Jim
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Spidertroop
Georgia
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From a safety standpoint you should make sure that your shutoff arrangement doesn't interrupt power to the trailer's braking system breakaway switch when you are traveling. Relative to using multiple batteries in a bank or independently, there are advantages and disadvantages of each method as indicated by the previous postings. Having multiple batteries serviced by the same charging system while also being connected to a common discharge load does indeed have the potential for cells becoming unbalanced if they don't all share the same characteristics/specifications. You will enjoy a longer service life if they are of the the same age, capacity and state-of-charge when they are first interconnected.
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La_Bolt_Fan
Los Angeles, CA
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Thanks so much, points taken!!
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opnspaces
San Diego Ca
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sorry had to add one more. Both ways will work fine. But if you run them separately the one may run down faster. If that happens you get the pleasure of getting out of bed to flip the switch to keep the heater on. 
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Adam-12
Northern CA
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One more thing.....when you get ready to buy two NEW batteries (because the ones you currently have will eventually require buying new ones), go out and buy two "golf cart" 6 volt batteries instead.
Hook the two up in "series" (different from hooking them up in "parallel" as is the case with your 12Volters.).
Batteries in series is as follows: Battery #1 pos+ connected to Battery #2 neg-. Battery #1 neg- hooked up to chasis ground. Battery #2 pos+ is your "hot" lead.
For example: Picture in your mind a 2 cell "D" sized flashlight. With two Duracell batteries each being 1.5 volts when connected together as outlined above (aka: "series"), those two batteries now make 3.0 volts. (1.5 + 1.5 = 3.0 volts). Well the same goes for your two golf cart batteries connected in series. You have now created a "12 volt" system.
The advantage of using the "golf cart" 6 volt batteries instead of two 12 volt batteries is:
1) the cost of two 6 volts in parallel is way less expensive than two 12 volters.
2) the greatest advantage of this set up is the fact that the large 6 volt batteries provide wayyyyy more amp hours (AH). If you get the right 6 volt batteries, two of them hooked up together can give you the same if not more lasting power (AH)as say using 3 or 4 12 volt batteries running in "parallel."
The two 6 volts connected together (in series) will last a long long time. I get about 4 days of use in between necessary charges when using the two 6 volters.
Hope this helps.
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Spidertroop
Georgia
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La_Bolt_Fan said
"So I put in a second battery since we will probably never go to places with hookups, we like the privacy of being in the middle of nowhere"
You didn't indicate how you are charging your batteries...or if you charge them while you are in the boonies. Here's a suggestion that might be useful(since you have already installed two batteries with cutoff switches), presuming you are using 7-pin vehicle-to-trailer connectors. Consider putting a wiring pigtail that terminates in a 7-pin trailer-end connector on the 2nd battery , with a corresponding 7-pin vehicle-end connector attached to the cutoff switch assigned to that battery. (This presumes the cutoff switch is not mounted in or on the battery box). If you have a safe place in the rear of your vehicle to carry a battery (in its box), this arrangement would permit you to easily disconnect the unit from the trailer, put it in the back portion of your tow vehicle and plug the pigtail connector into your vehicle's trailer connector. You can then charge the battery while driving around in your vehicle while the trailer stays in your camping spot. After charging you can simply disconnect/remove the battery from the vehicle and plug it back into the trailer.
All of this manipulation injects a certain modicum of inconvenience when compared with having everything hooked up and automatic in an RV park. I also spend a lot of time in the boonies, and during cold weather keeping batteries topped-up to operate the heating system is vital.
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