Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. Today he discusses batteries for boondocking.
Hi, All,
We are purchasing a new travel trailer that comes with a 12V DC fridge. No propane option for fridge. Dealer has recommended installing a pair of GC15 6V batteries instead of the normal 12V deep cycle batteries, because we intend to use the camper mostly for boondocking/remote camping. I am concerned about running out of power overnight.
We will have a gasoline generator, but I am concerned about how long we will have to run the generator to recharge the batteries every day. Do I need to install solar panels to keep the batteries charged up during the day? Or will the GC15 batteries and generator work well for us? Other power draws on the 12V system will be lights, furnace fan, water heater ignition.
Thanks for your help! —Phillip
Dear Phillip,
Thanks for joining us on our new forum and the opportunity to provide some assistance with your batteries and boondocking!
RVers switching to 12V DC refrigerator
We have seen a wave of RVers switching to the 12V DC refrigerator and getting away from propane. I’m not sure we have had a long enough trial period to see if it’s working out. I’m still a fan of the old absorption refrigerator – but then, I was a fan of the rotary dial telephone and VHS, as well!
I looked up your GC15 6V description and it looks to be a Deka-brand 6-volt deep cycle battery with a 230 AH capacity. Connecting two of these in series (positive to negative) will give you the 12-volt capacity you need for your rig, but does not double the amp hours and it will stay at 230 AH. So I called my “go to” power and electrical guru, Mike Sokol, to get the skinny on not only the batteries but the 12-volt refrigerator and estimated run time duration. He has tested a couple of versions with Lithium batteries at 100 AH and found he could get 36-40 hours on one model and about 24 hours on a 10-cubic-foot model.
Here is what you need to consider
If your GC15 batteries are lead acid, as the models I found, you will only be able to use about 50 percent of the available amp hours, which means at about 115 ah. So you will be very close to what Mike tested as he used Lithium Ion batteries that can be drained down to almost 100 percent. Also, what other 12-volt appliances and operations will be drawing from the batteries such as lights, vent fans, water pump and any appliance running on LP. Especially a furnace that will take a lot of 12-volt power with the blower fan.
The recommendation for the two 6-volt batteries versus the traditional 12-volt was a good suggestion/ A typical 12-volt deep cycle battery will only provide about 100 amp hours. So even two connected in parallel will only provide 200 amp hours, which is less than your 6-volt. Plus, 6-volt batteries are superior in materials and performance. However, your concern about recharging is legitimate as it will take 6-9 hours to recharge your batteries depending on the type of charger you have.
So, yes, I would suggest a solar panel array from someone like Zamp Solar or Go Power, both of which have a good charge controller. I would recommend the portable models, as you can park your rig in the shade to cool the interior down 20+ degrees and put the portables out in the sun. I would also suggest reviewing this chart to understand the power draw from the various 12-volt features.
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##1736
Hey Mike,
I hope it’s you.
Two years after switching from 6v golf cart batteries to lithium iron phosphate batteries, it has been my experience that they are far superior in every way.
They provide a higher voltage which makes everything on the RV function better, hold a more constant voltage and provide 12 volts up to the point they are completely discharged. With my 60 amp power converter/charger, I can recharge 2 completely discharged 100amp hour batteries in 4 hours. That isn’t theory, I have done it. I chose Battle Born Batteries but assume other brand lifepo4 batteries are similar. I don’t see ever going back to lead acid batteries.
I have 360 watts of solar panels and if in the sun they keep the batteries charged if I don’t have to run the furnace excessively. I have an absorption refridgerator. During mild weather all I need is a source of water and a place to dump every couple of weeks.
The 50% discharge rule for batteries isn’t a big deal! The rule of thumb is:
“If you subject a deep cycle battery to 80% DOD on a regular basis you will get roughly half the life out of your battery than if you were to cycle it to 50% DOD”
—https://www.batteriesinaflash.com/deep-cycle-battery-faq
You only pay a 20% financial penalty on total lifetime ampHours out of the battery. Here’s a simplified example:
100ampHour battery at 50% discharge = 50 ampHours @ 4 years= 200 lifetime ampHours
100ampHour battery at 80% discharge = 80 ampHours @ 2 years= 160 lifetime ampHours
To me, the convenience of having the extra capacity for two years is worth the 20% financial penalty due to the shorter life. If I only need the extra capacity half the time, the penalty is only 10%.
What happens to the 12 volt compressor when it is running on less than 12 volts? As the batteries drain, the voltage goes down especially under load.
Good question so I looked it up. For Furrion 12 volt RV refrigerators, Their specs say:
“Input voltage: DC 12V (min. DC 10.5V to max. DC 17V)”
Wow, what’s with the anger here? Everyone who is an expert as these two previous commenters seem to be should start their own blog.
No lithium suggestion?
A 120 amp lithium is $1200 for 1 battery.
Sorry Dave, but you’re flunking Batteries 101. It is absolutely not true that “6 volt batteries are superior…” as you state. Every lead-acid battery is identical given similar construction. a 12v deep cycle battery is actually just 2 6v deep cycle batteries wired in series, in one case. It IS true that some lead acid batteries are superior to other lead acid batteries, but this common “old wives tale” about 6v units is just that. I suggest you ask your friend Mike to give you a primer on batteries, so you can better advise your readers.
Don, as in most engineering choices, it depends. The average 12-volt battery is not a true deep-cycle battery, especially if it’s CCA rated. And 6-volt batteries typically have thicker plates that can withstand more abuse and the occasional deeper discharge. So in general 6-volt batteries may be able to provide more energy for boondocking, depending on how you use them. There are many exceptions, of course, but battery selection has almost reached diesel vs gas truck status. Sounds like a great topic for an Ask-the-Expert video. I have a guy in mind…
For the same number of total amp hours, it’s generally better to charge two 6-v batteries in serial than two 12v batteries in parallel.
Parallel cells are more likely to get unbalanced.