Whether we like it or not, we are all dependent on electricity, to varying degrees. And so being able to provide power to our electrical devices is an important part of camper live. So it’s no surprise that you may be asking yourself, “what size battery do I need for my camper or RV?”
This is a common initial question that we all ask ourselves when we first begin building our camper’s electrical system. Nobody wants to run out of power in the middle of the night, far from civilization.
So if you’re asking yourself this question, you’ve come to the right place.
In this article, we will teach you how to calculate what size battery you need for your camper’s electric system. Yes, it involves some pre-planning and making a list table, but by the end, you’ll have an appropriately sized battery bank that adaqutely meets your energy demands.
So if you’re ready, let’s get to it!
By the end of this post, you should be able to answer the following questions:
When Calculating Your Camper Battery Size, List Out Your Devices
Everyone requires a different amount of electricity. Some people have multiple computers, others have water heaters, and some have professional camera & drone gear for their work.
So the battery size of one person’s camper van may not be the appropriate size for someone else. We’re all different!
Below, we provide a simple 5-step guide to calculating your unique ‘daily energy usage’, which in turn will help you calculate your camper battery size.
After each step, we provide an example table that we created for our own battery sizing calculations when we built our camper van.
List Out Your Electrical Devices
The first step is to list out all the electrical devices you plan to have in your RV or camper.
Example Table 1 (Devices Only)
|Diesel Heater (winter only)|
Determine Each Device's Power Consumption
This part is a bit tedious, but you’ll need to figure out the amount of power (Watts) required by each of your devices.
You can usually find estimated wattage information either on the device itself, the product manual, or even on the Amazon product information page.
If you still can’t find a device’s power usage, you can refer to our own energy usage table below.
Example Table 2 (Devices + Watts)
|Diesel Heater (winter only)||20|
Write Down The Time Duration For Each Device
The next step is to write down for how many hours you plan to use each device. Numbers must be written in hours.
Fractional numbers work here. So, for example, if you plan to use your blender for only 5 minutes each day, you would write down ‘0.083’ hours.
Fancy math: 5 min/60 min = 0.083
Example Table 3 (Devices + Watts + Time)
|Load||Power (W)||Time (h)|
|Fridge||55||6 (on 1/4 of time)|
|Instant Pot||750||0.125 (30min every 4 days)|
|Diesel Heater (winter only)||20||5|
Multiply Each Device's Watts & Hours
In order to calculate each device’s daily energy usage, you’ll need to multiply the device’s Watts by the number of hours it will be used per day.
The result is the total daily Watt-hours (Wh).
As a final step, add up all the Watt-hours from each individual device to get your total Wh.
In the table below, your can see that our total watt-hours is 1,011.6Wh.
Example Table 4 (Devices + Watts + Time + Watt-Hours)
|Load||Current (W)||Time (h)||Daily Energy Usage
|Fridge||55||6 (on 1/4 of time)||330|
|Instant Pot||750||0.125 (30min every 4 days)||93.75|
|Diesel Heater (winter only)||20||5||100|
Lastly, take your total Watt-hours and divide the number by 12 (if you are using a 12-volt battery). Divide by 24 if you are using a 24-volt battery.
The resulting number is “Amp-hours (Ah)” and is the unit commonly used to measure battery size. We’ll refer to this figure as your ‘daily energy usage’.
Remember your total Amp-hour figure. You’ll need it for the next part.
How To Calculate Your Camper Battery Size
Now that you have your daily energy usage (Amp-hours), you can now calculate what size battery you need for your camper.
However, to do this, you will need to decide whether you will be using traditional lead acid (AGM) or Lithium (LiFePO4) batteries. This is critical.
The reason why choosing your battery-type first is so important is because different battery chemistries can be safely discharged to different levels. So if you select a battery-type that should only be discharged no more than 50% (for the sake of battery longevity), you’ll need a larger battery bank to account for this.
Want to know more about battery chemistry differences? Check out our AGM vs Lithium battery post to learn about the pros and cons of each battery type.
Calculating Battery Size With LITHIUM Batteries
If you decide to purchase lithium batteries to provide your power needs, the battery calculation is straight forward.
Example 1: If your estimated Daily Energy Usage is 35Ah, doubling it will result in 70Ah. Then rounding up will give you 100Ah. You would be safe in simply purchasing a single 100Ah lithium battery.
Example 2: If your estimated Daily Energy Usage is 80Ah, doubling it will result in 160Ah. Rounding up will give you 200Ah. You would be safe to purchase 2x100Ah lithium batteries.
Calculating Battery Size With LEAD ACID (AGM) Batteries
Deciding to purchase lead acid batteries instead will make the battery calculation just a bit more tricky. But still simple enough.
Example 1: If your estimated Daily Energy Usage is 35Ah, doubling it will result in 70Ah. Doubling it again will result in 140Ah. Then rounding up will give you 200Ah. You would be safe in purchasing 2x100Ah lead acid batteries.
Example 2: If your estimated Daily Energy Usage is 80Ah, doubling it will result in 160Ah. Doubling it again will result in 320Ah. Rounding up will give you 400Ah. We would then recommend buying 4x100Ah of lead acid batteries.
Overestimating Your Battery Bank, If You Can, Is Good
By following the above rules, you will have an appropriately sized battery bank sufficient to supply your energy needs.
But if it’s within your budget, overestimating your battery bank size and picking up an additional battery is encouraged because there will be days where you won’t be able to charge your batteries back to full. Perhaps it’s a shady day with no solar potential, or you’re boondocking with no shore power. Either way, overestimating your battery bank will help reduce your risk of running your batteries down to 0% and being without power.
Why It's Important To Correctly Calculate Your Battery Bank Size
We understand. Going through the process of creating your own electrical device table and doing all the math is tedious!
Why not just simply buy a battery or two and just be done with it?!
Well, we can think of three reasons why doing the work now will be worth it in the future.
By calculating your power requirements, you will better understand how many batteries and how many solar panels you will need. You can then design your campervan floorplan to build around these electrical requirements.
Without calculating your electricity needs, you risk building an electrical system that cannot sustainably meet your energy demands on a daily basis. You risk depleting your batteries and running out of electricity when you need it.
Batteries that have been discharged too low and for too many times will degrade faster and eventually die prematurely. This means additional costs are needed to purchase new batteries to replace the ones that have died.
How Our Own Energy Calculation Compares To Real World Data
For 4 days, we disconnected our solar panels from our campervan electricity system and we measured the flow of amps out of our batteries using our Victron Battery Monitor. We wanted to see how our real-life energy usage compared to our calculated estimation.
Below is a table showing our results.
|Jan 15, 2021 @10pm||Start|
|Jan 16, 2021 @10pm||864.00 Wh|
|Jan 17, 2021 @10pm||784.08 Wh|
|Jan 18, 2021 @10pm||999.36 Wh|
|Jan 19, 2021 @10pm||747.96 Wh|
From the above data, it looks like our calculation was quite close to our real-world energy usage. Figures do vary from day-to-day for a variety of reasons, but it’s encouraging to see that within +/- 163 Wh (+/- 16%), we are keeping within our calculated budget.
Recommended Battery Products
Batteries are the foundation of any campervan electrical system. If your budget allows, we recommend buying good quality batteries, whether they are Lead-Acid (AGM) or Lithium-Ion based.
Connecting Your Batteries To Your Solar Panels
We created a 100% FREE resource detailing the installation process of a campervan electrical system.
Step-by-step, from start to finish.
Conclusion: Size Your Campervan Electrical System In Advance
We hope this article has helped inform and inspire you to begin building your own campervan electrical system.
In this post, we discussed WHY having an electrical system in your campervan is important and HOW to begin calculating your daily energy usage. Most importantly, from this information, we discussed how BIG of a battery system you will need.
Once you have properly sized your battery bank, you may be wondering how many watts of solar panels you need to help keep your batteries regularly and sufficiently charged.
We discuss this in our next post: Determining The Size Of Your Solar Array.
If you have any questions or comments after reading our campervan battery and solar post, please let us know in the comments below!
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