Can two 6-volt house batteries run a 2,000W inverter?

Dear Dave,
Will two 6-volt batteries connected in series run a 2000-watt invertor? —Pat, ’02 Lance 835 Lite

Dear Pat,
When you connect the 6-volt batteries in series (positive to negative) you get a 12-volt bank but you do not double the amp-hour capacity. Batteries come in different amp hour sizes such as group 24, 27 and 31, which means they have anywhere from 110 amp hours of power to 185 or more. However, the lead-acid and AGM battery can only be discharged 50%, so you would only have 50-100 amp hours. You can connect a 2000W inverter to those batteries; however, it will drain the battery very quickly. Most 2000W inverters are connected to at least 200-amp-hour batteries or more.

How much power do you need?

To understand how much time you will get out of your batteries through the inverter is difficult to calculate unless you know exactly what is running in the RV. Go Power! has a good sizing chart that helps you sit down and calculate what would be running and for how long.

(I realize this is hard to see especially if you are reading this on your phone. You can get a pdf file on their website if it’s easier to see.)

It’s not an exact science as you don’t know if your 6-volt batteries are sulfated and not performing to 100% capacity. You are most likely “guessing” at how often you run the lights, how often the refrigerator compressor runs, and other 12-volt components in the rig. Your truck camper has smaller appliances and less of a 12-volt draw, but still way more than what two 6-volt batteries can supply.

How the inverter works

Here is why the inverter draws 12-volt power from the batteries and provides 120-volt power to specific items. Many of our readers state they just want to power a couple of outlets for the TV or a CPAP machine in the bedroom. However, you are no doubt boondocking (dry camping) if you need the inverter and are not connected to a 120-volt source such as a campground pedestal or generator.

Your inverter is going to draw the 12-volt power and only provide 120-volt power to a few outlets. BUT since you are dry camping, all your other 12-volt components are going to draw the batteries down such as lights, roof vents, water pumps, and every other appliance that runs on propane. Those need 12-volt power to run the module boards and open gas valves. The biggest draw is the furnace fan. This is why this calculation exercise is so important to help you identify all the components that will be drawn from the batteries.

This is an 1,800W Xantrex inverter in the 2015 Thor we are working on. It originally came with four 6-volt batteries connected in series and then parallel, which provided 600 amp hours but could only use 300 amp hours since they were lead-acid. They sulfated quickly and the original owner installed two Interstate 12-volt batteries, which provided 300 amp hours but they would not last more than two hours as the refrigerator was a 120-volt residential.

Since it had a traditional WFCO converter/charger, it didn’t take long for them to sulfate and bloat out.

Replaced with lithium batteries

We replaced them with two 12-volt lithium batteries and they spent two days boondocking this fall with full power. The unit is nestled away for the winter so we are looking forward to testing the longevity this summer.

You most likely will not be using a full 2000W for an hour straight with your truck camper, but boondocking on a chilly night will drain those batteries in a couple of hours if not sooner. My recommendation is to up your battery capacity and, if you are boondocking, look at lithium batteries. They are about 3x more expensive, but they can be drained down to almost 100% of amp-hour capacity and the quality ones like Expion360 have a 10-year warranty so they are a more cost-effective solution over time.

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Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

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