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12V System Guide for Camper Vans & RVs (With Wiring Diagrams)

For many camper van conversions, the 12V system is the most critical piece of the electrics. This encompasses the auxiliary (or “house”) batteries and the devices that are powered directly from these batteries without the help of any voltage converters (i.e., inverters).

12V DC power from a battery can power lights, usb sockets, fridges, diesel heaters, air compressors, smartphones, and fans.

If this is your first time building a 12V system, you might feel overwhelmed by the sheer amount of information to learn and the components to piece together. There is quite a lot to do, and safety is paramount!

This 12V guide is a free resource for assembling your own 12V ‘DC’ system in your camper van. We’ll help you size your system to meet your power needs and recommend all the necessary tools and materials for your installation. We’ll also include helpful wiring diagrams and graphics to ensure your system is built quickly and safely.

Beginner’s note: If you are a complete novice to everything related to electrical, we recommend starting with our comprehensive camper van electrical guide. It starts from the very beginning and provides a top-level view of every topic, including solar, inverters, and alternator charging. This post is just for the 12V ‘DC’ portion.

So, if you’re ready, let’s dive into it.

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Why 12V Systems Are Essential

Since your batteries already operate on 12V power, it is the most power-efficient to identify electrical devices that also operate on this same voltage so that they can be run directly from the batteries.

Power inefficiency: Electrical devices powered from the battery via an inverter would lose 10-15% efficiency because the inverter requires power to convert the voltage. In a camper van, being efficient with your power usage is essential because power is not unlimited (unlike traditional homes connected to the power grid). Skipping the inverter, as much as possible, minimizes your power loss.

A 12V battery powering 12V lights and an inverter powering 120V lights. Power is being utilized more efficiently with the 12V lights.
Power is lost when sent through an inverter

Key takeaway: Prioritize 12V products instead of their 120V counterparts. Get a 12V fridge instead of a 120V fridge. Buy a 12V fan instead of a 120V model, and so on. 120V products should only be used if there is no 12V alternative.

Choosing 12V Batteries

Auxiliary batteries are the heart of your van’s 12V system. They store and distribute the power required to run each device. Please read our comprehensive camper van leisure battery guide for a detailed overview of everything battery-related. Below, we summarize the essential information from that post.

Lithium vs. AGM

Batteries come in different types, like lithium and AGM. In virtually every scenario, however, you should be buying lithium batteries. Their prices have decreased drastically over the years and are not nearly as expensive as they used to be. Below, we compare the two battery chemistries and highlight the most important differences.

AGM1Lithium2
Power capacity100Ah100Ah
Weight64 lbs (29 kg)23 lbs (11 kg)
Sensitivity to sub-freezing?3NoYes
# of charge cycles45004000
Cost (upfront)5190300
Cost (per charge cycle)$0.38$0.075
Better deal?YesYes!

Table Footnotes:
1. Renogy 200Ah x 12V AGM battery
2. LiTime 100Ah x 12V lithium battery
3. Lithiums cannot be charged if below freezing.
4. Lithium @ 100% DoD & AGM @ 50% DoD
5. Prices in March 2024

Key takeaway: AGM batteries might cost less upfront, but because of their much shorter lifespans (number of charge cycles), lithium batteries are considerably cheaper in the long run.

Recommended Batteries

Which batteries do we like? Our battery recommendations fall into three categories.

  1. Premium lithium. This type of battery is for those where money is no concern and premium quality, customer service, and warranty are prioritized. Batteries are usually assembled in the USA or Europe.
  2. Budget lithium. This battery is for those who still want to invest in a quality lithium battery, but getting the most value for every dollar spent is essential. Batteries are usually made in China.
  3. Budget AGM. This is for those with extremely tight budgets, and saving every dollar is mission-critical.

Our opinion: Get a “budget lithium” battery. With an extremely low “cost per charge cycle”, budget lithiums represent the best value on the market today. “Li Time” batteries have been frequently taken apart and reviewed to have genuinely high-quality parts and assembly. We have also personally reviewed the Li Time “TM” lithium battery and came away similarily impressed.

Premium Lithium
Budget Lithium
Budget AGM

You get what you pay for. Batteries made in the USA with premium components.

Top recommendation. Get the power of lithium at a great price. Will Prouse on YT loves Li Time batteries, and so do we.

Weize AGM batteries are often the lowest price on Amazon. We recommend for extreme budget builds.

Premium Lithium

You get what you pay for. Batteries made in the USA with premium components.

Budget Lithium

Top recommendation. Get the power of lithium at a great price. Will Prouse on YT loves Li Time batteries, and so do we.

Budget AGM

Weize AGM batteries are often the lowest price on Amazon. We recommend for extreme budget builds.

Battery Sizing

It is essential to have an adequately sized battery bank that meets your power demands. With too little battery capacity, you risk running out of power. To help determine your ideal size, download our free battery calculator below.

For a step-by-step tutorial, please read: How to size a camper van battery bank.

12V System Installation Guide (5 Steps)

This chapter will show you how to build the same system as the diagram below. It might seem daunting at first, but we will take a methodical, step-by-step approach and introduce each of the products we use here and their purpose.

Complete camper van 12V wiring diagram connecting leisure batteries to 12V devices
Complete 12V wiring diagram for camper vans

If you are concerned about wire gauge, fuse sizing, breaker sizing, and general electrical safety, we will cover these throughout our post.

Just need the product list? Our 12V parts list provides a complete itemization of everything we use and recommend. This list is intended to be used alongside our electrical wiring ebook, which is completely free to download.

Step 1: Wiring Multiple Batteries Together

In this step, we’ll show you what you need (wires, components, & tools) to connect multiple batteries. This is essential to increasing your battery bank’s power capacity. (If you only have one battery, you can skip this step).

If you are building a 12V system and using 12V batteries, which we recommend, you should wire multiple batteries in parallel. This increases the power capacity without increasing the voltage.

To wire multiple batteries in parallel, connect each battery’s positive terminals together with red wire and each battery’s negative terminals together with black wire. The result should resemble the graphic below.

Three auxiliary batteries wired together with unknown wire size.
Which wire size to use?

Recommended Battery Wire Size

The size of the wire you’ll need to connect multiple batteries depends on the amount of electrical current (amps) that will flow through those wires. The greater the amps, the thicker the wire required.

The ‘technically correct’ method: To calculate the total amps flowing through the battery cables, you must sum the wattage (W) of every electrical device in your camper van. Then, divide this total wattage by 12 to get the total amps. Take your total amps and refer to this wire amperage chart to determine the ideal battery cable size.

The better method: For a faster, simpler, and safer approach, follow our wire size recommendation below, which is based on the wattage rating of your chosen inverter.

  • No inverter: 2 AWG
  • 1000W inverter: 1/0 AWG wire
  • 2000W inverter: 2/0 AWG wire
  • 3000W inverter: 4/0 AWG wire

Unsure what size inverter? Jump to our inverter calculator for a quick size recommendation.

The brand we recommend most for battery cables is Windynation. These wires comprise 100% pure copper, stranded conductors encased in thick EPDM rubber insulation for high-temperature resistance. Windynation is based in the USA, and each cable is handcrafted at its workshop in California.

No Inverter
1000W Inverter
2000 Inverter
3000 Inverter

35mm²

55mm²

70mm²

120mm²

No Inverter
1000W Inverter
2000 Inverter
3000 Inverter

How To Connect Electrical Wire to the Batteries

A red and a black wire attaching to the positive and negative battery terminal posts via lug terminals.

You must crimp lug terminals onto the wire end to connect the wire to the battery. This is not a tricky process, but you will need the correct tools and learn about lug sizing. Please read our lug crimping tutorial for a quick, informational guide.

Most batteries use 5/16″ terminal posts. If you connect the batteries using a 2/0 AWG wire, you will need 2/0 – 5/16″ terminal lugs. We recommend these lugs from Wirefy, a US-based company that ensures high-quality copper lugs for maximum electrical transmission.

Wirefy | Lugs (2/0 x 5/16")

This specific copper lug size (M8) crimps onto 2/0 AWG wire and connects to most battery terminals and inverters. These are pure copper lugs for efficient power transfer.

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By the end of this section, your batteries should look similar to the wiring diagram below, with electrical wires connecting to the batteries via lug terminals.

Three Redodo lithium batteries wired in parallel.
Three lithium batteries wired in parallel

Step 2: Wiring the Batteries to the Bus Bars

Now that the batteries are wired together, you are ready to connect the batteries to the positive and negative bus bars. After completing this 2nd step, your system should resemble the wiring diagram below.

What are bus bars? Bus bars are power distribution and collection centers. They allow you to connect other devices (e.g., 12V fuse panels, inverters, and solar charge controllers) to your batteries.

Wiring diagram connecting 12V leisure batteries to bus bars
Wiring 12V batteries to bus bars

Recommended Wire Size

Like in the previous step, the wire size you’ll need to connect the batteries to the bus bars depends on the number of amps passing through the wires. The greater the amps, the thicker the wire required. As mentioned earlier, we recommend sizing the wire based on the size of your inverter.

Avoid cheap wires. Our wire sizing recommendations assume you will use 100% pure copper wires. Copper-clad aluminum (CCA) wires are cheaper but transmit fewer amps at the same thickness as pure copper wires.

Recommended Components

Below are the four components we recommend for connecting the batteries to the bus bars. Our 12V parts list provides more detailed information for each product, including video reviews.

 
 
 
 

Protects wire from overheating.

Disconnects battery from electrical system.

Displays battery state-of-charge percentage.

Power distribution & collection

Protects wire from overheating.

Disconnects battery from electrical system.

Displays battery state-of-charge percentage.

Power distribution & collection

ANL Fuse Sizing

The ANL fuse protects the wire from overheating. The fuse ampacity rating you’ll need depends on the wire size you selected earlier. The thicker the wire, the larger the fuse rating required. Use the list below to identify which fuse size you need based on the wire size you are using.

Recommended Lug Terminals

You will need lug terminals to connect your wire to the recommended components. Some components (e.g., ANL fuse) require lugs with a 5/16″ ring diameter. Other components (e.g., battery switch, battery monitor, & bus bar) require lugs with a 3/8″ ring diameter.

Review the color-coded lug size chart below and refer to the previous “battery to bus bar” wiring diagram to see where each lug is used.

Two lug terminal sizes. One, in dark orange has a 3/8" ring diameter. The other, in peach color, has a 5/16" ring diameter.

Note: You must finalize your wire size BEFORE buying the lugs. If you are using 2/0 AWG wires, the lugs below will work.

Step 3: Wiring the Bus Bar to the 12V Panel

The next step is to connect the bus bars to the 12V fuse panel. This panel distributes the 12V power from the batteries to each 12V device, such as the lights, fan, fridge, and more.

This diagram shows how to connect the bus bars to the 12V fuse panel. Below the diagram, we’ll help you select the correct wire size and components.

Wiring diagram connecting bus bars to 12V fuse panel
Bus bars to 12V fuse panel

Recommended Wire Size

We recommend 4 AWG wires to connect the bus bars to the fuse panel. Windynation rates its 4-gauge wire at 150A, but the Blue Sea Systems fuse panel we recommend is rated for 100A. This means the wire will not limit the fuse panel, which is what we want.

Blue Sea Systems also recommends using 4 or 6 AWG wires. We use the larger wire for maximum safety.

12V fuse panel specifications from Blue Sea Systems indicating that 4 or 6 AWG wire must be used to connect to the panel.
Blue Sea System’s fuse panel specifications

Like the battery cables, we recommend Windynation-branded 4 AWG wires. With an extremely high strand count of 100% pure copper conductors, these wires provide maximum flexibility and temperature resistance.

Windynation | 4 AWG Wire

100% stranded copper wire. Rated for 150 Amps of continuous current and is ideal for connecting the bus bars to the 12V panel. Resists UV, water, oil, and salt corrosion.

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Recommended Components

You will need a circuit breaker and a 12V fuse panel to complete this wiring section. We recommend spending a few more dollars on a good-quality fuse panel from Blue Sea Systems. A fuse panel constantly receives and distributes 12V power, and you don’t want the plastic from a cheaper model to melt and shut down your van’s electrical system (we’ve seen it happen).

 
 

Protects 4 AWG wire from overheating. Watch YouTube review.

Distributes 12V power from the batteries to each end device. Watch YouTube review.

Protects 4 AWG wire from overheating. Watch YouTube review.

Distributes 12V power from the batteries to each end device. Watch YouTube review.

Why a 120A circuit breaker? The manufacturer recommends a maximum 125A fuse/breaker in their wiring schematic. So, a 120A breaker will be effective.

Blue Sea Systems fuse panel wiring schematic indicating a maximum fuse rating of 125 amps.
Blue Sea Systems fuse panel wiring schematic

To complete this section, you will need lug terminals with two different ring diameters (3/8″ and 1/4″). Refer to the lug size color chart below and locate the corresponding lugs in the earlier wiring diagram.

Two lugs with 4 AWG neck sizes. The dark green lug has a 3/8" ring diameter and the light green lug as a 1/4" ring diameter.

We recommend getting a lug terminal variety set, which covers 2 to 8 AWG wires, to save money. This set includes the 1/4″ and 3/8″ lugs you’ll need for this section and other lug sizes for different parts of the electrical system (e.g., solar, inverter, and alternator charging). Without a lug set, you would end up buying each lug size separately, which is more expensive and wasteful.

Sanuke | Lug Terminal Set

Save money with this convenient lug terminal set. It covers 12 different lug sizes from 2-8 AWG wires and M6-M10 ring diameters. Heat shrink is also provided.

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Step 4: Wiring the 12V Panel to Each Device

In this step, we connect the fuse panel to each 12V device. The diagram below shows the wires and components needed to complete this section.

Wiring diagram connecting the 12V fuse panel to individual 12V devices
12V fuse panel to 12V devices

Recommended Wire Size

14 AWG wire is the ideal size for connecting all 12V devices to the fuse panel. These wires can handle up to 180W of power (15A) at 12V, which is more than enough for each device.

We recommend getting 14/2 AWG “twin wire,” which means two 14 AWG wires (red and black) are encased in a white outer jacket. This jacket protects against driving vibrations, sliced cables, and short circuits.

GS Power | 14 AWG Wire

Get this 14AWG wire for all your 12V device connections. We like the tough outer jacket that protects the inner wires from the constant vibrations when driving. These tinned copper wires are 'marine grade' for superior resistance against corrosion.

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Avoid voltage drops for longer circuits. If the circuit between the fuse panel and the 12V device will be longer than 20 feet, consider upgrading to 12/2 AWG wire to combat voltage drop across long wiring distances.

Recommended Components

You’ll need the following components to connect the fuse panel to each of your 12V devices. Refer to the earlier wiring diagram to see where these components are placed.

 
 
 

Crimps onto 14-gauge wire and connects to the 12V fuse panel.

Extends the red & black wires from each 12V device to the fuse panel.

Insert these blade fuses into the appropriate slots in the 12V fuse panel to complete each circuit.

Crimps onto 14-gauge wire and connects to the 12V fuse panel.

Extends the red & black wires from each 12V device to the fuse panel.

Insert these blade fuses into the appropriate slots in the 12V fuse panel to complete each circuit.

Blade fuse sizing: Blade fuses come in different ampacity ratings. To calculate the correct fuse size for each 12V device, find the device’s peak current draw and round up to the next fuse size. For example, the Maxxair vent fan uses a maximum of 5 amps of power. Rounding up to the next fuse size gives us 7.5A.

Step 5: Grounding The 12V System

The last step is to connect the inverter to a designated ground point on the van’s chassis.

Connecting the negative bus bar to a ground point on vehicle chassis with 4 gauge wire.
Grounding the 12V system with 4-gauge wire

Ground Wire Size Recommendation

The size of the ground wire you will need depends on the size of your inverter. The list below will help you identify your ideal wire thickness based on the size of your inverter.

  • 1000W inverter: 6 AWG wire
  • 2000W inverter: 4 AWG wire
  • 3000W inverter: 2 AWG wire

Lug Size Recommendation

The lug sizes you’ll need to connect the ground wire to the inverter and chassis will depend on your wire size and the ground connection point on your vehicle’s chassis. We recommend this same lug terminal variety set as earlier to ensure you have the required sizes. This set is also helpful for other electrical system parts (e.g., 12V, solar, & alternator charging).

How To Locate a Ground Point

Your van’s user manual should help you identify a point on the vehicle’s chassis appropriate for grounding the inverter. Below is an excerpt from our Ford Transit’s handbook indicating the location of all 35 approved ground points.

Ford Transit ground points on the chassis
Ford Transit ground points

Popular 12V Devices

You decide which 12V devices you want to put in your camper. Below, we list the six most popular 12V device groups for camper van builds.

LED Lights

Usefulness: 9.5/10
Energy Draw: 0.17ah per puck light

Installing lights that run on 12V is a great way to brighten up your van’s interior when natural sunlight isn’t sufficient. We recommend installing a pack of LED Puck Lights in your camper’s ceiling. They’re bright, provide warm colored light, and draw only a tiny amount of power from your batteries.

Top Recommendation
Acegoo | 12V LED Lights

We use 12 of these 12V puck lights in our camper van. They fill the van with bright, warm white light and only consume 3W per device. Slim profile means they take up minimal ceiling space. Easy to wire to batteries.

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To learn more about installing LED puck lights in a van ceiling, visit our other post, How to install a beautiful cedar plank ceiling.

Puck lights not what you’re looking for? Check out these two other popular alternatives.

Ventilation Fan

Usefulness: 10/10
Energy Draw: 0.25ah when on low

A roof vent fan is a must when living in a camper van. Vent fans not only help bring in cool, fresh air and expel stale air, but they also help regulate the internal temperature of your van and eliminate greasy smells when cooking.

We leave our vent fan on 90% of the time while we’re in the van.

Best of all, if you choose the MaxxFan, the product comes with a built-in rain cover, so you can even use the fan when it’s raining. In our experience, a rain cover is critical.

Maxxair | Maxxfan Deluxe

A high-quality vent fan is a top van life essential. It exhausts stale, greasy, & musty air and promotes fresh air flow into the van. The Maxxfan's unique rain cover allows you to continue operating the fan even when it's raining hard outside.

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Want to learn more? Read our MaxxFan product review.

12V Sockets & USB Ports

Usefulness: 9.5/10
Energy Draw: N/A (depends on what is plugged in)

Having at least one pair of USB and 12V sockets is invaluable for van life. With sockets like these, you can power many different electrical devices, from smartphones to desktop fans, 12V fridges, USB propane detectors, cameras, portable inverters, and even aromatherapy diffusers. The list is endless.

We’ve installed three pairs of these USB & 12V combo sockets throughout our van, which are constantly in use.

Qidoe | USB & 12V Sockets

Great charging outlet that supports standard 12V ports and USB A & C. Suitable for all iPhones and Android models and 'Quick Charge' ready.

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12V Fridge

Usefulness: 9/10
Energy Draw: 0.72ah

A 12V fridge is an under-appreciated appliance in many camper builds. Good quality RV fridges aren’t cheap and can take up valuable space inside a van. However, having a refrigerator is necessary when planning to live and travel long-term in a camper. Compared to cheaper coolers, having a proper 12v fridge keeps your food cool 24/7, eliminates the need to look for ice every 2-3 days, and allows you to boondock in the countryside for much more extended periods.

We love our 12V Dometic fridge and wouldn’t go any other route to keep our food cool. To learn more, check out our Dometic fridge review!

Top Fridge Recommendation
DOMETIC 45-Liter 12V Fridge

A 12V fridge is a top van life essential. It keeps food cold & fresh and allows us to wild camp for more days. We recommend getting a top quality fridge with a durable compressor, electric components, and frame. Our Dometic fridge has handled all the crappy roads we've driven on.

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Diesel Heater

Usefulness: 9/10 in the winter
Energy Draw: 1.7ah

Installing a diesel heater in a van is a luxury item, but it’s incredible how well they work, how fuel efficient they are, and how comfortable they can make winter van life.

We were stuck at a campsite in Grand Canyon National Park for two days after 2 feet of snow fell all around us. Though temperatures dropped to 9F (-13C) at night, we were still warm & toasty inside. Our diesel heater has also made getting up in the mornings so much easier because, with just a push of a button, our van heats up in minutes.

Top Value Pick
12V Diesel Heater (Budget)

Keeping the camper van interior warm when it's cold out is a top priority. And this Chinese-made diesel heater can help you keep warm at an extremely affordable price. Comes with automatic high-altitude adjustment for up to 16,000 feet.

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To learn more, check out our post, How to heat a camper van during winter

Water Pump

Usefulness: 4/10
Energy Draw: 1.7ah

A water pump is a convenient item to have when it comes to van life. We installed one because we wanted our camper van to feel more like a natural home with instant running water with just a flick of a switch. If we could build a second van conversion, we would 100% install a water pump again.

Check out our other post to learn more about installing a water & plumbing system in a camper.

Top Pick
SHURFLO Water Pump

Compact electric water pump for camper vans & RVs. Can be installed in any direction and comes with attached wires to connect to the leisure batteries. Pair with filter, accumulator, and silencing kit to complete installation.

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FAQ

Should you have a 12V or 24V system in a camper van?

Although both 12V and 24V systems are popular in van conversions, most first-time builders should focus on building a 12V system. It is simpler and requires fewer parts and voltage conversions.

What are the best wire sizes for a 12V system?

14 AWG wire is the most popular size when wiring to each 12V device. For circuits longer than 20 feet, consider upgrading to 12 AWG wire. For wiring between the batteries and fuse panel, consider using 4 AWG wire.

What size battery for a camper van 12V system?

A 200Ah 12V battery bank (2400Wh) is a popular size for most camper van 12V systems. However, a larger battery bank will be required for van conversions with larger electrical demands. Refer to our batter size calculator for more information.

What voltage do most camper vans use?

Most camper vans install a 12V system. This is sufficient to power the lights, vent fan, fridge, water pump, and many other devices directly from the batteries. 24V systems are also popular but may require additional components, like a voltage converter.

Conclusion: Add Solar Panels & An Inverter Next!

Congratulations on reaching this point and successfully finishing your 12V system installation! This is no small feat.

But there is more to build than just the 12V system. If you want to power standard household appliances, you must install a power inverter. Or, if you charge your leisure batteries, you’ll need solar panels and a DC-DC charger.

We recommend reading our guides below for the following steps to extend your electrical system’s functionality.

Or, if you’re looking to start from the beginning, visit our ultimate camper van electrical guide, where we take you from start to finish. And by the end, you’ll have a robust & multifaceted electrical system that resembles the diagram below.

Complete electrical wiring diagram connecting leisure batteries to 12V devices, solar panels, inverter, and DC charger
Complete camper van electrical wiring diagram

And that’s it for this post. For additional 12V information, continue reading below, or if you have any questions, please post a comment in the section below.

Happy building!

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