What Size Battery You Need For Your Camper – How To Calculate

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Figuring out how much battery you need for van life is one of the initial questions we all ask ourselves when planning our camper van build. And this is for good reason. Running out of power is no fun and can be a real hassle!

And whether you’re planning a simple build or a mega resort on wheels, it’s critical to understand your power requirements so that you can calculate what size battery you’ll need for your camper.

So if you’re wondering how to do all this, you’ve come to the right place.

In this article, we teach you how to calculate what size battery you need for your camper. And by the end, you’ll have a battery bank that will meet your energy demands.

So if you’re ready, let’s get to it!

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    Step 1:

    List Out Your Devices

    Van Interior - Working Space

    The first step is to list out all the electrical devices you plan to have in your RV or camper.

    Good Tip: Making your list on a spreadsheet, like Excel, is helpful for future calculations.

    Below is the table we put together when doing our own battery size calculations.

    Table 1: List of Devices

    Ventilation Fan
    LED Lights
    Smartphone 1
    Smartphone 2
    Laptop 1
    Laptop 2
    Water Pump
    Instant Pot
    Diesel Heater (winter only)
    Hair Dryer
    Electric Toothbrush

    Step 2:

    Calculate Daily Energy Usage

    This part can be tedious, but doing your best accurately calculate your daily energy usage is critical to accurately sizing your battery bank.

    This is how to do it.

    1. List Each Device's Power Consumption

    First, figure out the amount of power (Watts) required by each of your devices.

    You can usually find this wattage information either on the device itself, the product manual, or even on the device’s Amazon page.

    Save time: Refer to our own energy usage table below to get your watts information.

    Table 2: Devices + Watts

    LoadPower (W)
    Ventilation Fan2
    LED Lights13
    Smartphone 112
    Smartphone 212
    Laptop 165
    Laptop 265
    Water Pump57
    Instant Pot750
    Diesel Heater (winter only)20
    Hair Dryer800
    Electric Toothbrush1

    2. List Time Duration For Each Device

    The next step is to write down for how many hours you plan to use each device each day. 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 hours

    Table 3: Devices + Watts + Time

    LoadPower (W)Time (h)
    Ventilation Fan220
    LED Lights137
    Fridge556 (on 1/4 of time)
    Smartphone 1122
    Smartphone 2122
    Laptop 1652
    Laptop 2651
    Water Pump570.17
    Instant Pot7500.125 (30min every 4 days)
    Diesel Heater (winter only)205
    Hair Dryer8000.042
    Electric Toothbrush15

    3. Calculate Total Daily Watt-Hours (Wh)

    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) for each device.

    Once completed, 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.

    Table 4: Devices + Watts + Time + WH

    LoadCurrent (W)Time (h)Daily Energy Usage
    Ventilation Fan22040
    LED Lights13791
    Fridge556 (on 1/4 of time)330
    Smartphone 112224
    Smartphone 212224
    Laptop 1652130
    Laptop 265165
    Water Pump570.179.69
    Instant Pot7500.125 (30min every 4 days)93.75
    Diesel Heater (winter only)205100
    Hair Dryer8000.04233.6
    Electric Toothbrush155
    Total:1011.6 Wh

    4. Divide Total Watt-Hours by 12

    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’.

    In Our Case: We divided 1,011.6Wh by 12v and got 84.3Ah. This is our estimated daily energy usage.

    Remember your total Amp-hour figure. You’ll need it for the next part.

    Step 3:

    Choose Your Battery Chemistry

    AGM vs Lithium-Ion Batteries

    If you haven’t done so already, now is the time to decide which battery type you want to go with. Your choices are:

    Why Does Battery Type Matter?
    Battery type matters because lithium and AGM batteries can be safely discharged to different levels. The more you can safely discharge a battery down to, the smaller the overall battery bank size you need.

    If you’re not sure about the differences between the two types, check out our AGM vs. Lithium post.

    But, if you really just want to know which battery you really should be using, read our other post on why lithium batteries are worth it for van life.

    Step 4a:

    Calculate Battery Size With Lithium

    If you decide to purchase lithium batteries to provide your power needs, the battery calculation is straight forward.

    Example: If your estimated Daily Energy Usage is 80Ah, doubling it will result in 160Ah. Rounding up will give you 200Ah for your ideal battery size.

    Step 4b:

    Calculate Battery Size With AGM

    Deciding to purchase lead acid batteries instead will make the battery calculation just a bit more tricky. But still simple enough.

    Example: 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 for your ideal battery size.

    Step 5:

    Add Another Battery (If Budget Allows)

    By following the above steps, you will have an appropriately sized battery bank sufficient to supply your energy needs.

    But if it’s within your budget, adding an additional battery is encouraged. This is because, in reality, it’s common to go multiple days without being able to properly charge your batteries.

    If you can even add just one additional 100Ah battery, this can go a long way to stretching out your energy independence.

    Proper battery size is only half the battle. Make sure you also have the right amount of solar wattage.

    Real World Data:

    Comparing Our Calculation To Reality

    For 4 days, we disconnected our solar panels from our van’s electric 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.

    Day (@ 10pm)Power Consumed
    Jan 15, 2021Start
    Jan 16, 202172 Ah
    Jan 17, 202165.34 Ah
    Jan 18, 202183.28 Ah
    Jan 19, 202162.33 Ah

    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.

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    Why Correct Battery Calculations Are Important

    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 floor plan 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.

    Recommended Batteries

    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.

    Best Lead Acid (AGM)

    VMax AGM

    Not the cheapest on the market, but this heavy duty AGM is built with solar charging in mind. Longer lifespan than usual lead acids at at 125Ah, more storage capacity than normal.

    Best Lithium-Ion


    Quickly becoming a campervan favorite, we have three of these in our campervan and love them. 2+ years on the road and they still work great and provide solid power to all our devices.

    Did You Find This Van Life Tip Helpful? We have lots of other useful articles to help you travel better in your camper van or RV. Check out our Electrical System Guide to read more great van life content!

    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.

    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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