How long will the residential refrigerator in my RV run when not traveling or hooked up to shore power? Can I assume it will be fine overnight at a rest area? —Randy, 2022 Flagstaff 8529RLS
To be blunt, you cannot assume anything. Instead, you need to calculate what your power draw is from the refrigerator and anything else that might be running, the amp hour rating of your battery or batteries, and their condition to hold a charge.
First, about the battery
Let’s start with the battery or batteries. Most RV manufacturers do not provide a house battery or batteries as these can be a huge price point between the standard 12-volt lead acid battery and lithium. They generally let the dealer spec the battery that would best fit their customer’s needs.
If your rig came with a stock battery, it is most likely a group 24 lead acid battery that will not power your refrigerator overnight. You need up to a group 27 or group 31, or maybe even lithium. A lead acid battery will only allow you to drain down to 50%, so the group 24 that only has 105 amp hours only provides 52.5 amp hours.
The lithium will allow you to drain it down 100%, so a 100 amp-hour battery provides the full 100 amp hours. If you don’t want to go to the expense of a lithium battery, you can add a second battery parallel and double your amp hours.
Then you need to consider the condition of the batteries as they need to be charged with a multi-stage charger that has a bulk charge to break up sulfation, then an equalizing and float charge. Most converters simply charge the batteries at 13.6 volts and drop to 13.2 volts to maintain. That does not condition the battery or batteries and they will sulfate and lose their ability to store power.
It is hard to tell the stage of condition in a traditional battery as the only method is to charge them to full capacity, let them sit for a while, then attach a 25-amp draw machine and count the hours. Nobody does that other than Lifeline batteries, that I know of.
So if you have lead acid batteries, I would charge them up and do an overnight test run to determine how long it will run to see what your batteries are holding. You will need something in the refrigerator, so put a sealed bag of ice in the freezer and several containers of water in the refrigerator.
What else will be using the power from the batteries
Now we need to calculate what all will be drawing from the batteries while not connected to shoreline power. You should have a data plate on the refrigerator that will tell you the draw. A typical 8 cu. ft. residential refrigerator will run about 8 hours on a typical lead acid battery, according to several trips and demos I have done.
However, if you are boondocking, other appliances and items will also pull power such as the water heater, any lights you have on for periods of time, the LP leak detector, roof fans/bathroom vent, onboard water pump, furnace, and any other items that run on LP or 12-volt power. So it will not be just the refrigerator if you are staying in the rig. So the 8-hour run will be shortened by how many people in the rig use how much stuff and for how long.
Another variant is temperature. The higher the temperature, the more the refrigerator will be “cycling” or running, which means the more power it will use.
Go Power! has a very good calculator that will get you started on realizing what components might be running and for how long. There is no exact science, but this is a good exercise to get acquainted with the power these components draw. Find it on their site here.
So, there is no perfect answer without knowing battery power, condition, and other components running. However, I hope these steps can help identify those items and help calculate how long you can dry camp or boondock.
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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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