How long will RV batteries last boondocking

The existing flooded lead-acid (FLA) batteries in our coach are original and just over six years old, bulging quite a bit, and barely run our typical load overnight before being more than 50% discharged (which isn’t great for FLA batteries). That makes boondocking a bit of a challenge since it usually means running the generator a couple of hours in the morning and evening. It was time to figure out how long will the battery last dry camping. Don’t have time to read this now? Pin it for later! We only recommend products we love and your support means a lot to us! This post contains affiliate links and if you make a purchase after clicking on our links we will receive compensation at no additional cost to you.

Boondocking

Determining Battery Capacity

After a bit of research on batteries and looking up specifications, here is what I figured out. The six 6V 220 amp-hour (AH) batteries wired in series + parallel makes a 12V system that has 660 AH. Proper battery maintenance says to only discharge them to 50% capacity, aka state-of-charge (SOC), to ensure a long lifespan so that means their usable is really only about 330 AH. The problem is that it’s a bit of a guess what the SOC % is at any given time with our current system which consists of only a 2,000 watt Magnum MS2012 inverter/charger and a basic ME-RC50 remote to view and configure settings. Without additional modules for the Magnum system, we can only see what the battery bank voltage is in real-time which can give you a rough idea of what the SOC % is by doing a little math.

Voltage vs State of Charge

For example, if your 12V battery bank reads 12.65 volts that is near 100% and 11.9% is about 0%. Anything lower than 11.9% you’re seriously damaging the battery life. You’d think that just determining the midpoint on voltage would be 50%, but it’s not that simple since capacity is affected by temperature (colder than 77 degrees = less, warmer = more), the types of batteries you are using, and if you have a load on the batteries (like we do ALL the time) then it will show a lower voltage than the resting voltage which is when nothing is using the batteries for a period of many hours… vice versa with a higher voltage if you’re charging plus other factors. Oh, and the inverter is only 80% efficient so you lose some power in the conversion from 12V to 120V. You can read all about battery science here. I had to pore over that and a half dozen other articles for a few hours before I understood it.

In addition to what the real-time battery bank voltage is, the existing ME-RC50 remote gives an estimate of the load in/out while inverting 12V DC to 120V AC, but the manual says it’s only accurate +- 20%. Not very accurate! In our case, it was usually reporting a load of about 12-15AH which was to power appliances like the laptops and refrigerator (and other things you plug into standard wall outlets throughout the RV like a coffee grinder, toothbrush chargers, webcams, etc). To make it more challenging, there is no way to see what the DC 12V draw is directly off the batteries for things like the ceiling lights, water pump, etc. Those things don’t require the inverter to run.

Total Capacity vs Usable Capacity

If you’re following along and doing the math, you can see 12 hours at say 15AH load for the inverter = 180AH used (12*15=180). With 330AH usable on the battery bank, that means we still should have 150AH after twelve hours minus whatever that unknown 12V DC load is using. However, in our experience, a typical dry camping day goes like the following: We arrive at a campsite around 3-4 pm, do our thing in the evening then go to sleep and our batteries are way below the 50% voltage mark by morning. So either the actual load is much higher than we are estimating, or our batteries are old and no longer have the charge they did when new.

Maintenance

Plus we have no idea how the previous owners treated them since certain types of batteries require proper care and maintenance or else they can also fail early. Our batteries are just “cheap” flooded lead-acid type so they typically have a 5-7 year lifespan and are of the higher maintenance variety. You have to open caps on them once every month or so and make sure they have enough distilled water. They are on a pullout tray so this is fairly easy to do with a funnel and a headlamp. They make easy pump refill caps but they are $50 for every two batteries!

Fortunately, there is a solution to get more accurate numbers. We decided it was time to add a battery monitor kit, replace our RV house batteries and upgrade the inverter remote. Read about that in our RV House Batteries article.

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