Evaluating How Long Your RV Battery Will Last Off Grid

I spent some time analyzing data from the history of my solar panels, looking at their performance during different types of weather. I only looked at how much sun the panels were getting. I did not look at the temperature. I have 3 arrays with 965W on my roof but for analysis I decided to focus on just the stock 165W Furrion solar panel. I took the data I collected and used it to show a relationship among different types of Sun conditions and different types of loads on the battery. I used this to show how long the battery will last. I post a lot about RV power systems and I have received many questions about this. I recently wrote an article that goes along with this one as the content is a continuation of what I wrote about there. I will include a link to that article at the bottom.

So basically I again used a standard, dealer supplied, 100Ah lead acid battery that has a usable capacity of 50Ah. An explanation of Amp Hours (Ah) is also linked below.

I looked at the average gain in Ah supplied by the Furrion 165W panel during the most sunny days and fully overcast rainy days. I also looked at the average fair weather day. I broke this down into 4 categories.

An ideal sunny day with a gain of 55Ah. This is about as good as it gets with the panel performing an average of 85% for a full 5 hours.
A mostly sunny day with some passing clouds. The daily gain is 49Ah.
A sunny day with some clouds but still a good day. The daily gain is 34.3Ah
Finally, a rainy, highly overcast day with a very poor daily gain of only 9.1Ah.

This is all based on real data collected from my Victron system. I would have included a general overcast day but the data is so variable on those days that I decided not to include it.

I also looked at the energy needed to run the most basic things in our RV. This includes the 12V refrigerator and lights in the evening. In addition I also added using the ceiling Vent Fan because it is commonly used. Data tables do not include all the extra stuff that could be draining energy from the battery. There really is no way of quantifying this in a useful, general manner. I chose the things we all use and excluded the things I can not validly determine. Please keep this in mind when looking at the data tables.

Table 1. Shows that if only the refrigerator and lights are used and the days stay sunny, the RV battery will run continuously. Of course there will be other drains but, if kept at a minimum, it can be done.

Table 2. Shows that if it rains for more than 2 days, the battery will not make it to the 3rd day.

Table 3. Shows that on a same type of day as Table1., if you use your fan you will not make it into day 3.

Table 4. Shows that if that day is mostly sunny you may make it through your 3rd day if you use your fan less than shown in Table 3.

Table 5. Shows that in ideal conditions, you will make it through day 3 but the 4th day may be pushing it.

This data was not meant to disappoint you. The purpose of this analysis and write-up is to inform and help support those of you who have a stock RV battery and solar panel setup. If you are planning on long drives and then connecting to power at a campsite, you are all set. You will have enough power to keep your food and beer cold on the drive and in most cases with an over-night or two off the grid. The battery from your truck will aid in the battery charging. However, if you plan to be off-grid for longer than 2-3 days you need to either be super energy conscious or find an alternative. There are 3 ways to increase your energy availability. (See my article on RV Power Systems for more information about this.)

The first is with a generator. In my opinion a generator is a must-have as a backup but for durational off-grid use it is not a sustainable option.

The next options are to increase your battery size or to increase your solar panel size. Again, I have written about this in detail in the above mentioned article. However, this article is about helping with decision making about how to increase your time off-grid in the most efficient manner, based on your needs.

The considerations of increasing battery capacity and/or solar power really is based on your personal needs. I used Google Sheets to create a page that you can use to help determine the effect of changing Battery size, Power consumption, and Solar panel wattage. Basically what I did was take one of the above tables and make it interactive. You write in your Battery size, Estimated energy use and Solar panel size. It will return, like the above tables, the remaining battery capacity and the number of days you will continue to sustain power. This goes up to 7 days.

I also included a tool that you can use to enter your solar panel wattage to and see the approximate amount of energy in Ah you may get under each weather condition. Use this to get the value to enter in the “Addition from Solar” box.

Please realize that this is just a helpful tool that is designed to give good estimates. There are way too many variables to guarantee its perfect accuracy. However you can look at what effect doubling your battery or solar or both. For example you can plug in a 200Ah battery and a 100W solar panel to see how long it will sustain you off-grid.

Link to Interactive Data Table

Link to my setup data at Victron VRM Portal

Link to my Article about RV Power Systems

Link to the article I wrote that inspired me to write this one

Stock Solar with 12V RV Refrigerator Not Charging Battery

Link to What is an Amp Hour Ah? A beginners guide