2 - 6 volt batteries wired in series to create 12 volts? Is that what I am seeing here? If so, why wouldn't you do 2 - 12 volt batteries wired in parallel? Wouldn't that give you longer run time at the same voltage?

There is a solar panel wired to it. Would that make any difference?

 

The reason that it's commonly done this way is that inexpensive true deep cycle 6V batteries are available pretty much everywhere. At least as far as I know. Have a look at the reserve capacity on whatever 12v deep cycle batteries you are considering.
Trojan t105 is "the" 6V battery and its good for 225 amp hours (at the 20 hour rate)

I dint know what's out there, but the first three 12v deep cycle batteries I found had 20 hour rate capacities of 75, 90 and 100 amp hours. So even with two its less than the setup of two t105.

 

Dual 6 volt batteries is fairly common. I'll probably go that route when I have to replace my dual 12 volt batteries.

 

Well that would make sense. I don't know a whole lot about batteries. It is very blurry, but in the bottom left of the pic I am pretty sure it says 210 amp hours. I have a very good battery store (like they only sell automotive style batteries) close to me. When i need new ones which should still be a few years. I will go talk to them and revisit this.

Thanks for the info!

 

Looked up the specs of these batteries

Product Name:
US AGM 2000 Voltage:
6-Volt Sealed AGM
Data:
20 Hour Rate: 213
5 Hour Rate: 182
Minutes of Discharge @ 75 Amps: 124
Minutes of Discharge @ 56 Amps: 177
Minutes of Discharge @ 25 Amps: 475
CCA @ 0 Degrees (F) -18 Degrees (C): 710
CA @ 32 Degrees (F) – 0 Degrees (C): 855
Length: 10.24” (260mm)
Width: 7.09” (180mm)
Height: 10.79” (274mm)

 

I can't think of any engineering reason that two 12V in series wouldn't be a great solution if you can find 12V batteries with good specs at a price point you are happy with. I just know it's not nearly as common, and I'm pretty sure the cost is the issue because the 6V setups are cheaper.

 

It used to be the case that the two six volts actually provided slightly more amp-hours and with thicker plates offered more discharge/recharge cycles, but things like that are always subject to change. So yeah, a little more bang for the buck. I think for most folks the way they use their campers you end up splitting hairs.

Steve

 

Most of the serious dry campers use 2 6 or some of add 2 6 and then a change over switch to your second set of batteries.
...need a more efficient blower motor for spring and fall.
any how, Battery School | Batteriesnorthwest.com | Advantages and Disadvantages of using two 12 volt batteries connected in parallel or two 6 volt batteries connected in series. good site for battery info.

 

Thanks for the link. I read most of the items there. One big takeaway for me was that I need to disconnect my solar panel charger from the battery when I'm checking the water levels and adding water. I should also be wearing safety glasses when I do it. I need to verify how my dual 12v batteries are wired.

Let me throw out a question: If an on-board generator is present, is there really a need for an expensive battery setup?

 

depends,
number of items running off battery,
hours of generator running,,,, noise, fuel
number of days without shore power,
distance to a local fuel station.

I just added a portable generator,
and thinking about a second 12 volt battery.
mostly when its cold and need furnace overnight. 3 to 5 nights without shore power.
Wife has health and breathing problems. Asthma
so a somewhat warm area and to "Run" her 120 volt breathing machine when needed.
YES, I have an inverter also. 400 watt.

 

In general, the way most folks use their campers going campground to campground, the way the rigs come from the factory is perfectly satisfactory. It is only when living off the cord that adding a generator, solar, and inverter really pay off.

The furnace is usually the biggest single power pig when running on DC power. Normally you will see about an 8 -10 amp draw when it is running, with run time being a lot or a little depending on where you camp. A single battery may not be able to keep you in heat for even a night once the temperature dips down near freezing. Cold weather is the variable that is the most difficult for RVers to content with in terms of equipment.

Steve

 

Great discussion! I almost did not drop-in as the subject line was a little vague and thought that it was just another who-has-the-best-battery discussion. Perhaps a moderator can change the subject to something like 'Pro / Con of twin 6v versus parallel 12v'?

Toward the topic of furnace consumption of DC, one thing I do not see much mention of is using a catalytic heater. 0% power draw and 100% heat. Had a hard-mounted catalytic heater in another rig and I really miss it. Managed to go two nights in the upper teens on a set of parallel 12 volts with a wife that only cared about comfort and not power consumption ('cause the baby . . .). Were it not for that catalytic heater (and two tiny solar panels plus about an hour of charging from the truck), I remain convinced that we would have lost the furnace somewhere in the 2'nd night.

Another possible factor to limiting the furnace draw for older rigs is to switch over to a digital thermostat which has a tighter on / off range. The older thermal or mercury thermostats have a wide range and let the temperature fall quite a bit and then the furnace struggles to bring the temperature back up. If the temperatures are moderate (say, in the 50's or so) the older thermostats are not a huge issue. But in freezing temperatures with a thinly insulated travel trailer, a digital thermostat should help limit the power loss by reducing the cycle time from a tighter on / off range.

 

Jay,

Excellent point and often overlooked. We use a Cat in our truck camper as the furnace just overpowers the space and man I hate the noise of the furnace blower in both our fifth wheel and our TC. A Cat dialed back works much better. If going this route everyone bear in mind a Cat uses oxygen from inside the camper so the standard recommendation is to leave a vent open. A properly installed RV furnace burns only outside air. The Cat we use has an auto shut-off on it so if O2 gets too low it shuts itself down and CO detector is mandatory.

The 12 Volt versus 6 Volt debates may be getting passe with many of us going to AGM batteries from Sam's Club. Just makes life simpler. It is really easy to overinvest in a battery system that will never be used is my thought there and we actually do camp "off the cord" at times.

Steve

 

I don't have an inverter (yet!) so that didn't even enter my thought process. I can see where you better have a good set of batteries if an inverter is in use.

The other take away from that site was that older batteries need more water. I don't know if it's that I have a solar panel working every day to keep the batteries charged or that my batteries are indeed old. I've had to top up fill three cells in the past 3 months. I'm keeping a log of that just to see if one cell is more "needy" than others.

 

Yes, as they age, batteries do need to be watered more because they lose more as the charger works longer to top them off (charger keeps pushing until batteries push back and old batteries don't push back as well).

Steve