How to Charge Your Campervan Electrical System With the Alternator

By: Scott Adamson
/ September 9, 2022
Did you know you can charge your house battery with your van’s alternator while you drive? Let’s find out how!

When you’re living the vanlife, it’s easy to become hyper-focused on your battery and power levels. 

“Is everything charging properly? Am I getting enough solar power? Can I use my blender this morning?” 

Not having enough juice to power all your devices and appliances is a daily worry for many vanlifers. After all, electricity is the last thing you want to worry about when enjoying the countryside or attempting to live “off-grid”.

In this article, I’m going to share a very important ‘vanlife electrical’ tip to take some of that stress away – How to charge your house batteries with your alternator. I’ll highlight:

  • What is an alternator, how does it work, and what are its benefits
  • Different combiners that help charge a van’s electrical system
  • Recommendation for choosing the most effective combiner. 

What is an Alternator?

Your van comes with a built-in power generator; the alternator. The alternator’s job is to keep your starting battery charged so that it can power all of your van’s electrical needs (the radio, air conditioner, lights, and so on).

Now you’ve converted your van into a camper. 

Since your starting battery is not powerful enough to power all of your new household needs (your fridge, lights, fans, computers, etc), you’ll need to install house batteries (also known as secondary or auxiliary batteries) and charge those using an alternate source.

Most commonly, vanlifers use solar power to charge their house batteries (the second battery responsible for supplying power to these appliances). The most obvious drawback is that you don’t get any power when there is no sun. 

Another popular way is to charge your house battery with the alternator simply by driving around! 

Can My Alternator Charge My Auxillary Batteries?

Whether you can charge your house battery from your alternator depends on how big your alternator is. Typically, only 50 percent or half of your total amperes will be available to charge your house battery. 

This means that if you have a 220 amperes alternator in your van, you will have a maximum of 110 amperes available for your house battery charging. 

The reason for using the rule of 50% is because running your alternator at full output all the time will cause your alternator to shorten its lifespan and fail quicker

As alternators are quite expensive, you don’t want to wear them down.

FOR AGM Auxillary Batteries

The blue sea SI-ACR Charging Relay is a good option if you are looking for a robust relay to isolate battery charge for AGM house batteries. 

A few benefits include: 

  • Safeguards electric appliances during engine cranking
  • Compatible with 12V/24V systems
  • Supports high output alternator up to 120 amperes

The main benefit of using something like the Blue Sea Si-ACR is that when you start your vehicle, it will charge the vehicle battery first, once it recognizes that the vehicle battery is fully charged, it will then start charging the house batteries. This way, your start battery is always full. The second function is that when your vehicle is shut off, the SI ACR will disconnect from the house batteries so you can not drain the start battery while powering the appliances in the living area of the van. 

DC-DC Charger

A DC-DC charger, also known as a battery-to-battery charger, uses your main battery to charge your house battery (or batteries) quickly and efficiently. It uses a process known as bulk-absorption-float to maximize the charge in your house battery and ensure that it’s charged to the maximum.

This charging method is primarily used when charging Lithium house batteries using the alternator. Since lithium batteries are different chemistry than the vehicle start battery, the DCDC charger is able to properly charge the different battery types to avoid damage and provide proper charging profiles. 

It can do this by increasing the power and efficiently charging your van. You can easily get a 100% charge in your secondary battery with a full day of driving. 

If you are still confused about what a DC-DC charger is and how it helps you to charge your van’s electrical system, here’s a detailed article that you may find useful: What is a DC-DC Battery Charger?

Pros of DC-DC Charger

  • Efficient: The DC-DC charger efficiently charges your auxiliary battery by optimizing input from the main battery. 
  • Dual purpose: If you go for a DC-DC charger inbuilt with a solar regulator, it can charge your house battery simultaneously with solar power and the alternator.
  • Optimal charge: A DC-DC charger also controls voltage fluctuations providing an optimal charge to the auxiliary battery. 

Cons of DC-DC Charger

  • Expensive: The DC-DC charger is more expensive compared to a battery isolator. 
  • Technical: It also requires a certain level of expertise to install it correctly. 
  • Requires space: You will need find space in your electrical system area to place your DC-DC charger.

Which DC-DC should I choose?

Several brands make DC-DC chargers, including RedArc, Victron, and Renogy. All these brands have different pros and cons, which make them suitable for different users. Here’s how their feature and benefits line up 


  • Works well with different batteries, including lithium, AGM, and standard lead.
  • Advanced features such as the Maximum Power Point Tracking (MPPT) solar regulator charge the batteries using solar panels while you are driving.
  • Provides optimal battery charge by using a unique algorithm that provides specific charging profiles tailored for battery types. 
  • Click Here to Buy



  • Comes with a flexible multi-stage charger and built-in Bluetooth. 
  • Works well with both 12V and 24V systems, offering greater flexibility to different van users. 
  • Satisfactory performance in high temperatures up to 131 Fahrenheit (55 Celcius)
  • Click Here To Buy



  • Works well with various alternator types. 
  • Advance technology helps protect your main battery by identifying over-discharge. 
  • Optimizes battery charge by minimizing transmission errors. 
  • Includes protection from high temperatures and high voltage. 
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  • Includes an optional remote control to set up and use the charger.
  • Comes with an efficient design that is waterproof. 
  • Works well with different battery types, including lithium and AGM. 


We recommend RedArc because:

  • Dynamic nature and ability to withstand extreme climates. 
  • Optimizes charge to the secondary battery, maximizing its performance. 
  • It also works well with traditional charging alternator systems
  • Compatible with 12V/24V as well as smart alternators. 

Battery Isolators 

Isolators are also used to charge the secondary battery through the alternator by isolating the main battery from the secondary battery. Both the main battery and auxiliary batteries are connected, and the isolator is connected to the alternator. 

You can think of an isolator as a gateway that lets voltage pass only in one direction, so if the alternator is charging the main battery at 12V, it will also push the same power to the secondary battery. This means the secondary battery won’t drain your main battery by consuming its amperage to run the van’s electrical system. 

A battery isolator is more like an on and off switch 

Pros of Battery Isolators

  • Cheap: Isolators are relatively cheaper than DC-DC chargers.
  • Easy installation: They are easy to install and don’t require a lot of technical know-how. 
  • Fast charging: Isolators charge the battery at a constant and fast rate, replenishing it quickly.

Cons of Battery Isolators

  • Does not regulate voltage: One of the biggest disadvantages of battery isolators is that they don’t regulate the voltage to the auxiliary battery leading to under/overcharge. 
  • Don’t work well with lithium batteries: Battery isolators can’t efficiently manage amperage in lithium.


While there are many affordable battery isolators, we recommend the RedArc SPI 12. This solenoid battery isolator uses 12V with 100 amperes of ratings. It’s easy to install and compact in size. The RedArc SPI 12 also uses power-saving technology and fault indication for enhanced utilization.

Can You Use a DC-DC Charger in Conjunction with a Battery Isolator?

The short answer is yes! You can use a DC-DC charger and a battery isolator together. The first thing to notice here is that typically the main battery of the campervan is a lead acid battery such as AGM, while house batteries tend to be lithium because of their efficiency and long life.

Therefore, the battery isolator will always ensure there is enough charge for your cranking battery to start your engine. It will not regulate the amperage flowing to your auxiliary battery, therefore over/undercharging it.

To get around this problem, you will need a DC-DC battery charger that can manage the current flowing into the secondary battery. That’s why you can use a DC-DC charger in conjunction with your battery isolator to enhance your van’s electrical system and make it foolproof.

Benefits of Alternator Charging

Charging your van’s electrical system with the alternator has several key benefits. 

These are listed below: 

  • Fast: Charging your batteries through the alternator is relatively fast.
  • Passive Charging: You are virtually generating electricity when driving. This helps in making sure that the house batteries don’t drain out completely.
  • No dependence on the sun: Compared to solar power, which requires sunlight to generate electricity, an alternator does not depend on any external sources.
  • No plugging-in problems: Relative to shore power which requires installing an inverter and having a charging station nearby, the alternator will charge your batteries without any outside dependence. 

Key Takeaways 

You will feel better equipped with charging your van’s electrical system through an alternator as it’s a relatively easy and more reliable option for charging your house batteries. 

Here are a few key takeaways from this article:

  • You can easily power your van’s house batteries by driving around through your alternator.
  • Using a DC-DC charger or a battery isolator is an effective option. You can also use a DC-DC charger with a battery isolator to ensure better charging. The main benefit of using them together is for jump-starting.
  • RedArc is highly recommended for DC-DC chargers and battery isolators with excellent quality and flexible voltage. 
Scott Adamson
Wanderful Idea Guy
Coffee drinker, adventure seeker, below average photographer.
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