This post will cover everything you need to know about your campervan battery system. We will also talk about the three different ways to charge your batteries, and what each setup would look like. Use the list below to jump to specific topics. You can find links to all the components we used in our build in the van build shop. Remember, it’s perfectly okay to outsource the wiring of your van to a professional or have a professional inspect your work. We are not professional electricians so take our advice with healthy skepticism. This post contains affiliate links, we earn from qualifying purchases at no cost to you.
Before we get into the specific battery types, lets cover basic battery lingo.
Amp Hours / C Rating
The Amp-Hour rating or c-rating is a measure of the rate at which a battery is being charged or discharged. It is defined as the current through the battery divided by the current draw at which the battery would deliver its nominal rated capacity in one hour.
A C/1 discharge rate is a measure of the current drawn to fully discharge the battery 1 hour. For a battery with a capacity of 100 Amp-hours (AH), this equates to a discharge current of 100 Amps.
When sizing deep cycle battery banks, it is important to note that the Amp-Hour (AH) rating of the battery is calculated based on a full discharge and is not actual usable capacity. Deep cycle lead-acid batteries are not designed to be fully discharged.
State of Charge (SOC)
An expression of the present battery capacity as a percentage of maximum capacity. You will need a battery monitor that shows the state of charge, a simple voltage measurement is not enough to determine state of charge.
Depth of Discharge (DOD) (%)
The percentage of battery capacity that has been discharged expressed as a percentage of maximum capacity. Different battery types will have a maximum DOD. For example lead acid batteries can only be discharged 50% before they start to get damaged, lithium ion however can be discharged up to 95%. In practical terms this means if you have a 100 amp hour lead acid battery you can only us 50 amp hours before you damage your battery.
The resistance within the battery, generally different for charging and discharging, also dependent on the battery state of charge. As internal resistance increases, the battery efficiency decreases and thermal stability is reduced as more of the charging energy is converted into heat. Lead Acid batteries have high internal resistance which makes them less efficient.
Nominal Voltage (V)
The reference voltage of the battery, also sometimes thought of as the “normal” voltage of the battery. Most batteries you will consider are 12 volts and that is a very common voltage for a lot of DC electronics. The actual voltage coming from your battery could range from 14.4 – 10.5 depending on your state of charge. You may however want to explore the ‘golf cart’ route that uses 6 volt batteries.
The minimum allowable voltage. It is this voltage that generally defines the “empty” state of the battery.
The number of discharge-charge cycles the battery can experience before it starts to fail. The actual operating life of the battery is affected by the rate and depth of cycles and by other conditions such as temperature and humidity. The higher the DOD, the lower the cycle life.
The voltage that the battery is charged to when charged to full capacity. Charging schemes generally consist of a constant current charging until the battery voltage reaching the charge voltage, then constant voltage charging, allowing the charge current to taper until it is very small.
The voltage at which the battery is maintained after being charge to 100% SOC to maintain that capacity by compensating for self-discharge of the battery. Lithium Ion batteries do not like to be floated and therefore require different charging parameters.
The ideal current at which the battery is initially charged (to roughly 70 percent SOC) under constant charging scheme before transitioning into constant voltage charging.
There are three main types you should consider for your campervan battery system. Flooded lead acid (FLA), AGM and lithium ion. Each have unique considerations and pro/cons we explore below.
Flooded Lead Acid (FLA)
Lead acid batteries are the most traditional type found in most cars.
- Cost – They are the cheapest option on the list and can range from $100 to $300 each.
- Weight – The electrodes inside them are made of lead so its not uncommon for a typical lead acid battery to weigh more then 40 lbs each. Cargo capacity and weight distribution are important considerations in your van build and lead acid batteries wont be friendly to your MPGs.
- Maintenance – Must be filled with distilled water and the level of water must be maintained monthly. They also off gas a noxious chemical when they charge so they must be ventilated.
- Orientation – Must be mounted in an upright position.
- Efficiency – Lead acid batteries are roughly 85% efficient, meaning that if you have 100 watts of solar coming into your charge controller, the batteries are only soaking up 85 watts.
- Depth of discharge – 50% – meaning that your 100 amp hour battery only has 50 amp hours of usable energy
- Lifespan – 3-6 years. Lifespan is greatly affected by how the batteries are used and maintained
AGM stands for absorbent glass mat and are commonly mistakenly referred to as ‘gel’ batteries. We don’t recommend considering gel batteries for your campervan battery system. AGM batteries are just sealed lead acid batteries that don’t require maintenance, don’t off gas and are a little more efficient.
- Cost – AGMs cost roughly twice the price of flooded lead acid
- Weight – They weight roughly the same as flooded lead acid
- Maintenance – Permanently sealed and require no maintenance
- Orientation – Can be mounted in any position
- Efficiency – 85-90%
- Depth of discharge – 50%
- Lifespan – This again depends on how the battery was treated but they typical don’t last as long as flooded lead acid. 2-4 years
- Other Considerations – Resistant to vibration and work well in cold temperatures
Our Top AGM Picks
Lithium Ion (LiFePO4)
Lithium iron phosphate batteries are the newest chemistry available on the market and have a number of advantages over the other types of batteries. And no, they wont explode like a cell phone battery, that is a lithium polymer (LiPo) battery. The only bummer about lithium is they cannot be charged below freezing (they can discharge below freezing). One great development is that Battle Born has produced a heated battery which solves this problem in your van. Lithium is best paired with a battery monitoring system that monitors temperature and other parameters.
- Cost – Most expensive option. $800 to $1500 each
- Weight – Lightest option – ~31lbs
- Maintenance – No maintenance, no off gassing
- Orientation – Can be mounted in any position
- Efficiency – 99%
- Depth of discharge – up to 99% depending on the manufacturer
- Lifespan – 3000-5000 charge cycles or 8-15 years if properly maintained
- Other Considerations – Can not be charged below freezing, require special charging parameters
Our Top Picks for Lithium Ion
Sizing Your Campervan Battery System
How many batteries you will need to meet your power demands on the road? You’ll first need to know what type of battery you’re going to use ie. lead acid vs. lithium because if you have lead acid batteries then you can only use 50% of the rated capacity safely vs lithium where you can use up to 99%.
Then you’ll need to figure out the individual amp hour requirements for each component in your electrical system and add them all together. For example if your 12 volt fridge draws 2 amps while running and you estimate it to run six hours in a 24 hours period its going to consume 12 amps from your battery per day. If your lights draw .25 amps when turned on, and you estimate you’ll need them on 5 hours a day, they will consume 2.5 amps from your battery over a 24 hour period. By adding all the individual components together you can estimate how much power you will use per day and then be able to choose the correct battery bank size for you.
Here is a Google Sheet template to help calculate your energy consumption. Lets say your total power consumption is 75 amps hours per day. If you choose 200 amp hours of AGM, your actual usable energy is only 50% of that or 100 amp hours so you’d be very close to draining your batteries every day. If you had 200 amp hours of lithium Ion however, you can use 99% of that or 198 amp hours so you’d have more then two full days of power from your batteries before needing a charge. We recommend choosing to have at least double the amount of power you use per day in battery capacity.
A note about parasitic drain. Your batteries will always lose power due to heat and little inefficiencies here and there. You should assume that you’ll lose a few amps a day due to parasitic drain.
How you wire your batteries together will affect their performance. If you wire two 12 volt 100 amp hour batteries together in series you will double their voltage to 24 volts while keeping the capacity the same. If you wire the same two batteries in parallel you will keep the voltage the same (12V) but double the capacity to 200 amp hours. Note that some batteries cannot be wired in certain configurations, so check the manufactures recommendations.
Most campervan battery system run on 12 volts so if your using 12 volt batteries a parallel connection is for you. If you have chosen to go the ‘golf cart’ route with 6 volt batteries, then you will most likely want to use both series and parallel connections in your battery bank.
Battery Cables Size and Fuses
You’ll need some pretty heavy duty cables to handle the high current coming into and going out of your batteries and the fuses to match them. The main sets of cables to consider are (1) between the batteries themselves (2) from your battery to your inverter, (3) from your battery to your fuse block and (4) from any charge source such as a solar controller, DC/DC charger or shore power charger. Lets look at each of these individually.
Between the Batteries Themselves
Each battery will have maximum continuous discharge rating which will be used to determine the gauge of cable you need to wire them together. One thing to remember is to keep all battery cables the same length so one doesn’t have higher resistance then the others. Even though the actually amperage moving though your cables is likely to be much lower then the maximum your batteries can handle, it is always a good idea to have larger cables then necessary.
For example let’s say you have two 12V 100 amp hour lithium ion batteries with a max continuous discharge rating of 100 amps and you want to wire them in parallel. A parallel connection will double their capacity so you now have a 12V 200 amp hour battery. If these cells are rated for 1C, meaning they can discharge all of their capacity in 1 hour, then the cables need to be capable of carrying 200 amps. Using the chart below we can see that if you cable is less then 2.9 feet a 6 AWG cable will meet our needs. If it was up to me however, I would size up to a 4 AWG cable just for piece of mind. You do not need to wire a fuse between the batteries themselves.
Between the Batteries and Inverter
The wattage of your inverter will tell you how many amps it will draw from your batteries. If you have a 1000W inverter with a 12V battery it will draw 83A (W=V x A) if you have a 2000W inverter it will draw 167A. Using the chart below you can see we’d use a 6 AWG cable for a 1000W inverter and a 2 AWG cable for a 2000W inverter as long as the total wire run is less then four feet. The chart also recommends the correct fuse size that needs to go on the positive cable between you inverter and battery. Again I would go one gauge larger than recommend, but keep the fuse size the same. To learn more about inverters and how to choose one, visit this post.
Between you Battery and Fuse Block
Your fuse block will handle all the loads for your regular wiring such as lights, fridge, water pump, fans, etc. To determine the correct gauge of cable to go to your fuse block, you should calculate the hypothetical maximum current you could draw if all of your appliances happened to be running at the same time.
If you have already calculated how much battery capacity you need for your system (amp hours) using our google sheets template, then you already have the number you need. If not, use the sheet to add up all the power consumption of your appliances. Use this number and the chart below to determine the correct cable gauge. For example if you calculated 30 amps, a 10 AWG cable is best for you as long as the run is less then 6 feet.
To determine the fuse size for this circuit consult the chart below. For our 10 gauge wire example above a 50 amp MIDI fuse would be perfect.
Between Battery and Charge Sources
The final set of heave gauge wire to consider is between your batteries and any type of charge source such as a solar controller, DC/DC charger, alternator or shore power. Each of these devices will be rated for a maximum amperage and this is what you’ll use to determine the correct gauge cable.
For example, our MPPT charge controller is rated for 30 amps. Using the same charts we used to size our fuse block cables, you can see that a 10 AWG cable and a 50 amp fuse is correct for this application. One thing to careful of is the length of wire your using. If you need to run cable all the way up to your engine compartment for a battery isolator or DC/DC charger, the cable will have to be thicker because of the length.
For shore power applications it’s pretty easy. Whatever your charger is rated for, usually either 50, 30 or 15 amps, will determine the cable size. If the total run is less then 6 feet, 50 amp would require 6 AWG cable, 30 amp a 10 AWG cable and 15 amp a 14 AWG cable. All of these will require a fuse too!
Battery Cable Termination
Large gauge cables, such as the ones you’ll use on your battery, will also be terminated with a crimp connector called a lug. Just like purchasing OFC wire, you want to make sure to get pure copper lugs, instead of aluminum. The lugs shown below are called ‘flared starter lugs’ and you want to make sure the tool used for crimping is compatible with the type of lug you have.
The lugs will be stamped with two sets of numbers. On the photo to the left the numbers are 2-3/8. The number 2 refers to the gauge wire this lug is meant to be used on and the 3/8 is the diameter of the hole in inches. When buying lugs, (which are not cheap) make sure to pay attention to both of these numbers so you don’t end up with the wrong size. Here’s a link to an assortment of lugs.
To crimp these copper lugs the process is the same, it just requires bigger tools. You will need a lug crimper such as the ones below. The first tool on the left is meant to be struck with a hammer. I haven’t used one of these before so I cant speak to its effectiveness, but they seem to have pretty good reviews on Amazon. The tool on the right below is lever action and has a set of rotating dies that will accommodate the most common sizes of lugs. You just need to match the dies to the size of lug you’re crimping and press down on the handle as you would with bolt cutters. This is the style of lug crimper I’m familiar with and it worked well enough, although there is a technique that requires some practice to get right. Just go slow and watch how the die is pinching the lug, you might want to crimp with a larger die first then crimp again with a smaller die. You can also get hydraulic crimpers which seem to get good reviews.
Make sure to pull really hard on your lug after crimping it. Any movement at all is unacceptable, the lug should be permanently bonded with the wire. Use a heat gun to heat shrink over the crimped part of the lug and you’re done.
Battery Disconnect Switches
You will need a way to disconnect your batteries from the rest of your system for maintenance, storage or in the event of an emergency. A battery disconnect switch is the way to go. This should be located on the positive pole of your system immediately after the battery before any distribution blocks or bus bars. Consult our wiring diagram for an example.
How to Charge Your Batteries
There are three main ways to charge your battery system in your van, solar, from your van’s alternator, and shore power. You can implement any combination or all three methods into your build depending on your budget and needs.
Solar is a very popular way to charge your batteries and is surprisingly inexpensive, easy to install and requires minimal maintenance. We cover all the details of using the sun to charge your batteries in this post.
Using the vans alternator is also a very popular way to charge your batteries but requires some special consideration depending on your setup. If you are using lead acid or AGM batteries for your build, you can hook your vans alternator up using a battery isolator . A battery isolator acts as a middle man between your vans starter battery and your accessory battery bank. It insures that your starter battery never gets drained and regulates the charge from the alternator to maintain your accessory battery bank whenever your van is running.
If you have lithium batteries in your build you will require a DC to DC charger. Because lithium batteries require different charging parameters then lead acid, this device will regulate the amps from your alternator to properly charge your lithium batteries without damaging them.
Another consideration when using your alternator to charge your accessory battery bank is the alternator itself. Your van’s stock alternator probably isn’t going to be happy about trying to charge two batteries at once which may lead to premature failure or some hot wires. You may want to consider upgrading to a higher output alternator and thicker cables that can handle the increased loads.
Shore power is when you hook up your van to the main electrical grid at a house or campground. You might want this option if you plant to stay in a lot of campgrounds or are traveling in an area where the sun does not shine often. To do this you will need a charge converter or a inverter charger combo. I recommend getting a inverter charger combo because it will eliminate the need for a separate inverter and some other special components such as a transfer switch.
At a campsite you will commonly see hookups available for 15amp, 30amp and 50 amps. The 50 amp service is typically for large RVs running air conditioning and the 15amp hookup will only run one high powered device at a time so a 30 amp charger is a nice balance and will be able to handle anything you want in a typical van build. Its nice to carry a 15-30 amp adapter though just in case the campground you’re staying does not have 30amp service, you will still be able to use shore power.
Campervan Battery System Monitoring
A battery monitor will record all the electrons going into and leaving your battery using a shunt, then display a state of charge percentage so you know exactly where your system is at. I honesty didn’t think I needed a battery monitor because my solar controller showed me the voltage of my batteries but voltage isn’t the whole picture. In fact, it’s nearly impossible to tell the state of charge of lithium batteries just by the voltage alone. Besides SOC, a battery monitor will also monitor the ambient temperature of your battery bank. This is super important if you have lithium cells because they can’t be charged below freezing. A monitor will allow you to automatically disable charging below certain temperatures. Here is the battery monitor we have in our van.
My Two Cents
Flooded lead acid is old technology and does not have a place in modern van builds. AGMs are only marginally better but at least they don’t off-gas. If your budget allows it, get lithium ion. They will pay for themselves because of their long lifespan and you’ll be a happier camper, especially if you’re incorporating solar into your build. You should also invest in a battery monitor if you get lithium ion batteries.
Hope this guide gave you some value and cleared up the confusing world of campervan battery system. You can find links to all the equipment we used in our van build at our van build shop.