Sizing your battery bank appropriately is perhaps the most critical step when preparing your RV for off-grid living. At a minimum you’ll probably want to run essential electrical equipment for at least one day without recharging. With enough batteries you could even power an electric refrigerator, microwave oven, or an air conditioner.
So, how many Amp Hours (Ah) of battery capacity do YOU need? There’s no one-size-fits-all solution and figuring out the right battery capacity for your lifestyle will involve some trial and error. To start, you’ll need to ask yourself these questions:
- How much energy do you consume on a daily basis?
- How often are you able to recharge your batteries?
- How much space do you have for batteries?
- What is your budget?
How much energy do you consume on a daily basis?
How do you figure this out? Using a detailed spreadsheet to calculate your daily energy usage was the old-school way to figure this out, but few installers do this anymore.
Measuring the actual amount of energy used is another technique which requires special battery monitoring equipment. This is a great strategy if you already have a good battery monitoring system (BMS) installed. If you don’t have a battery monitor installed then this is pretty tough to accomplish.
Most installers these days focus initially on identifying large energy consumers (equipment like residential refrigerators) that will run continuously throughout the day and night. They are often referred to as continuous loads and will draw more power over time.
Estimating the daily consumption of these large continuous loads is key to developing a realistic power consumption baseline.
Installers and DIYers will then select a standard battery system configuration of 200, 400, 600 or more Amp Hours (Ah) and a suitable power inverter to meet the demand of the continuous loads plus smaller on-demand appliances and personal electronics.
Example: An RV with a residential refrigerator that consumes 130Ah per day will need at least 200Ah of usable battery capacity to keep it running. Power consumption from personal electronics, TVs, laptops, lights, etc. can be estimated. A battery bank with 400Ah to 600Ah of usable capacity is a good starting point.
Check out this article for several examples of standard off-grid RV system configurations.
What is usable capacity?
Usable capacity is the amount of usable energy that can realistically be drawn from your battery bank. This can be far less than the combined Amp Hour (Ah) rating of your battery bank especially if you have flooded lead acid or AGM batteries. Batteries may also degrade over time causing their usable capacity to drop.
We see a big difference in usable capacity when comparing traditional lead-acid batteries to modern Lithium batteries. Popular lithium iron phosphate (LiFePO4) batteries can provide up to 100 percent of their rated capacity. Traditional lead-acid batteries will only provide about 50 percent of their rated capacity and degrade faster as you put more load on them. This is simply a battery chemistry limitation.
Example: 200Ah of lithium batteries will provide roughly 200Ah of usable capacity while 200Ah of lead-acid batteries will only provide 100Ah of usable capacity. You’ll need to double the number of lead-acid batteries.
Currently most new RVs come equipped with traditional lead-acid batteries. So consider doubling the number of lead-acid batteries in order to achieve the usable capacity you’re looking for.
Lithium batteries can also sustain higher power levels under load, recharge faster and are one-third the weight of their lead-acid predecessors. In fact, making the switch from AGM to Lithium had a huge impact on our ability to boondocking with solar. I explain how in this video.
How many days can your batteries power your RV?
Having the ability to recharge and replenish your batteries each day is a good start. However, this is not always possible especially when charging with solar. If you have a day or two of cloudy skies you’ll need to cut back your power consumption to conserve energy or fire up a generator.
Here are some factors to consider
- Recharging from solar panels requires many hours of clear skies and sun
- Recharging from your engine’s alternator (or use a DC-to-DC charger) requires frequent driving and burns fuel
- Running a generator with a battery charger also requires fuel
Ideally, consider sizing your battery bank to provide two or three days of reserve capacity. If that’s not an option initially, then I’d recommend designing a system that can be scaled up if needed.
How much room do you have for batteries?
Space is often a limiting factor for how big your battery bank can be. When space is limited you may decide to just fit as many batteries as possible in the space provided.
Start by calculating the maximum number of batteries you have space for. Consider various sizes from different manufacturers and choose a battery layout that works best for your space. Take time consider lots of options and layouts. It will be time well spent.
If you decide to split you battery bank into multiple compartments, then try and follow these guidelines for best results:
- Keep a short distance between battery groups
- Use properly sized cable for safety and to minimize energy losses (voltage drop)
- Use battery cables of the same length when connecting the batteries
Consider lithium batteries to make efficient use of your space. Lithium batteries will give you more power per square inch (higher energy density) and can be mounted on their side as well as vertically.
Example: When designing the battery bank for our Class A upgrade, I switched battery manufacturers at least twice until I found batteries and a layout that gave me the most capacity for the space provided. I ultimately spent a little more but ended up with a high-quality battery configuration that I’m really happy with. To see how I did it watch this video.
Finally, don’t forget that you’ll also need room for a power inverter. It is best to install your batteries and inverter in the same compartment. You’ll minimize energy losses (voltage drop) by using shorter cable connections.
What is your budget?
The cost of the batteries is typically the biggest factor preventing folks from a battery bank upgrade. Back in the day, simply adding a second battery to your RV was the thing to do. Nowadays, we really want to power everything off-grid. This requires making a significant investment in batteries that will hopefully last a long time.
Lithium batteries have a much higher up-front cost compared to lead-acid batteries. Their longer lifespan makes them less expensive in the long run though.
What LiFePO4 batteries are good? Dragonfly Energy’s Battleborn Batteries are still considered the best-of-breed LiFePO4 batteries. Their quality and reputation is also reflected in the price. I’ve put Battleborn 100Ah and Gamechanger GC3 batteries in two RVs now, and they have been extremely reliable. Enduro is another US-based LFP battery maker that offers LFP batteries at a budget price. SOK is a highly rated Chinese-made LFP battery maker selling their batteries through US distributors.
Regardless of what brand or battery chemistry you use, I recommend planning for expansion. Start with a moderate setup that meets your needs. Install a good quality power inverter and battery monitoring system to track your power consumption over time. Then adapt your setup as needed. That’s exactly what I’ve done in our 15+ years of RVing.
In 2007 I started with one lead-acid battery. This quickly led to two in the first year. Then I switched to 6 volt golf cart batteries, then to four AGM 6-volt batteries. I ultimately made the switch to lithium batteries and haven’t looked back.
What to read next?
For a comparison of different sized off-grid systems, components and their costs, check out this article. If you’d like to see how I retrofitted the electrical system and lithium battery bank in our RV, then go to my downloads page and checkout my system diagram.