When I was setting up my motorhome I had no idea how many batteries I would need. Other than knowing I needed a deep cycle battery, I didn’t know much else about buying an RV house battery. I started off on a budget, buying two at a good price from contacts in the automotive industry. Over time my power needs grew and I now have a total of five batteries set up as three different battery banks. See how I set up my electrical system here. If you’re looking at buying an RV house battery, the number you need will depend on many things.
Batteries are expensive and this may be a limiting factor for some people. Another thing to consider is how often you will be using them. Is it for the odd weekend away, a couple of weeks at a time, or do you live in your motorhome full time? You need to think about what your power needs are going to be, although the problem with this, as was the case for me, is that over time your power needs might grow.
Your batteries are storing the power that you want to use. That means that you need enough to get you through the times when you have no battery charging capability – overnight if your batteries are charged by solar. This might be longer if you have a period of bad whether when your solar charging capabilities are limited by cloud.
So if you’re buying an RV house battery, how many do you need? Assuming budget isn’t a factor, it’s a good idea to buy as much as you can (within reason) and solar panels to match. (enough solar to top up your batteries daily) It’s good to know you have enough battery power and solar panels to not have to worry about your power usage. Check out this article if you’re wondering how many solar panels you should have.
The RV house battery set up in my van
As a guide, in my small van I’ve been using 200 amp hours of Lithium (12 Volt) and a 270 watt solar panel. This is running lights, a small Waeco 40 litre fridge, a laptop computer most of the day and charging two phones. The most I’ve seen the batteries drop is to 70%, meaning I’ve used 30% of the 90% capacity when using lithium batteries.
The RV house battery set up in my motorhome
In my motorhome I have three different battery banks. 100 amp hours of lithium bought from Sunny Tech Solar at 24V is powering the 255L Samsung Fridge and water pump. 200 amp hours of AGM at 12V is powering lights, stereo, laptop, monitor, charging phones, and the diesel heater. 100 amp hours of AGM is being used for charging small items, lights, cigarette USB items, spark for the gas oven, spark for the gas hot water.
The minimum amount of RV house batteries I’d want to have
As a minimum I’d want 100amp hours of lithium in a small van, and in a motorhome or RV I’d want 400amp hours of lithium. If you’re installing AGM batteries or similar, you pretty much want to double the amp hours of the lithium. So 200amp hours of Lithium minimum in a small van and 800amp hours of AGM in a motorhome. Read more about how to choose house batteries for your motorhome or RV here.
Use a formula to calculate your power needs
There are more scientific methods you can use- formulas to work out your power consumption. The idea as that you buy your RV house battery to suit your exact power needs. Work out everything you want to be powering in your motorhome, use the formula to see how much power they are going to use, and then buy your RV house battery and solar panels to match this number. Thats fine, assuming you already know what you’re going to use, your power needs don’t increase over time, and you’ve factored in the weather conditions, where in the world you are (daylight hours are location dependent) and know how long you’re going to use each item daily.
Gather ideas from other motorhomes, RV’s or vans similar to yours
My suggestion is to talk to people with motorhomes, RV’s or vans, similar to what you own or are building, ask them what sort of RV house battery they have, find out how it’s been for them, how many they have, and what powered items they use in their vehicle. It’s really worth getting to know a bit about the house electrical system in your motorhome, that way if you’re camped in the middle of nowhere and something fails, you’ve at least got a chance of restoring power yourself. This all assumes you’re working with 12 volt or 24 volt power supply. Not mains power.
How to Charge RV House Batteries
Solar panels are a great way to charge your RV house battery. The sun is providing you with free energy every day. Even on cloudy days your solar panels will still work. The output will be reduced, but as long as there is light you’ll get a small amount of charging. If you think you’ll be worried about charging on cloudy days, add an extra solar panel. Instead of 1amp of charging from the panel, adding a second panel would double it to 2amps on a cloudy day.
Although not a preferred option by many due to the noise, you can use a generator to charge your batteries.
How to Charge Your RV House Battery While Driving
You can charge your RV house battery using the vehicles alternator while driving. A device called a voltage sensitive relay (VSR) is used to allow charging of the vehicles battery and the RV house battery at the same time. When the engine battery reaches 13.7volts the VSR allows charging of the RV house battery. When the engine is stopped, the voltage drops and the VSR disconnects the RV house battery from the vehicle start battery. This protects the RV house battery from voltage spikes when starting the vehicle and prevents the vehicle start battery being inadvertently drained.
Gel, AGM and Lithium batteries all have different requirements for charging. You need a charge controller that you can input the correct charging settings for your type of battery. This is pretty simple to do on most charge controllers. If you’re using lithium batteries, make sure your charge controller supports their special charging requirements. See more about my charge controllers here. I look at the EPEVER charge controllers and the EPEVER Solar Station Monitoring software.