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In a Camper Van, you’ve already got a generator built-in. It’s called your alternator. Your vehicles battery powers all of the electrical devices that your vehicle needs on a day to day basis. Spark plugs, ECU, Fuel Pump, Air conditioner blower, radio, and much more. The alternator’s job is to keep that battery full.

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Now, you’re converting a van into a camper van and plan on installing ‘house’ batteries to run all of your household stuff like, lights, fans, refrigerator, computer and whatever else you’ve got going on.

For most people, their goal is to power these ‘house’ batteries off of solar, which is great! But when the weather gets cloudy and the charge gets low, it’s nice to be able to charge your batteries on a road trip from point a to point b.

A quick disclaimer:

Your stock vehicle alternator isn’t necessarily specifically designed to handle the huge loads that it takes to charge a huge house battery bank. This can over-tax your alternator and shorten it’s life. Our campervan and hundreds of others are operating on this same system, but it’s just something I need to make you aware of.

There are 2 ways to charge your house batteries with your alternator that we’re going to cover: Isolator, and battery to battery charger.

Quick note before we get started.  This is just one part of an overarching “How to Install a DIY Camper Van Electrical System” series.  If you’ve just stumbled on this article directly without seeing that, there are likely some things we’ve already covered.  If you want to check out that step by step guide, you can do that here:

Also, we have interactive solar wiring diagrams that are a complete, A to Z solution for teaching you exactly what parts go where, what size wires to use, fuse size recommendations, wire lug sizes, and all kind of other stuff to help save you time and frustration.  You can check that out here:

Charging DIY Camper House Batteries with an Isolator

An isolator simply connects your house battery bank to your starting battery. When you turn off your engine, the isolator, “isolates” the two battery banks so that when you use your lights, fans, refrigerator and such, you won’t kill your starting battery, leaving you stranded.

The isolator is simply a pass-through of power and it largely unregulated for the most part in terms of the voltage and amperage that gets sent to the house batteries. The voltage and amperage going to the house batteries is dependent on the voltage regulator and amperage output of your alternator.

Pros of Charging Camper House Batteries with an Isolator:

  • It can charge at a rapid rate, over 100 amps in certain cases.
  • Isolators are less expensive than battery to battery chargers
  • Isolators have the capability to jump-start a weak starting battery in emergency scenarios.

Cons of Charging Camper Batteries with an Isolator:

  • A lack of data makes knowing at what rate your vehicle will charge your house batteries nearly impossible. Making planning difficult.
  • Unregulated power tends to make people nervous during the learning phase.

Charging DIY Camper Batteries with a B2B (Battery to Battery) Charger

A battery to battery charger takes the voltage and amperage that is being put out by the vehicle alternator and regulates it down to a preset and constant amount.

Pros of Charging Camper House Batteries with a B2B (Battery to Battery Charger.

  • Can regulate amperage making system planning easier
  • Can deliver a specific ‘charging profile’
  • Ultimately a bit ‘safer’ than an Isolator

Cons of Charging Camper House Batteries with a B2B (Battery to Battery Charger.

  • More expensive than an Isolator
  • Bigger/bulkier than an Isolator
  • Slightly more difficult to wire than an Isolator

Battery Isolator vs B2B (Battery to Battery) Charger

Which is better? A battery Isolator or a B2B charger? A lot of resources tend to overexplain this with technical engineering jargon. My dad, when somebody was overexplaining something to him, would always say…

“Spare me the labor, just give me the baby”

So, “here’s the baby”: I asked Sean Nichols from Battle Born Batteries which was better for their Lithium Batteries regarding a BIM (Isolator) vs B2B Charger. He said:

“I like the BIM (isolator). It is simpler, quieter and takes up less space. Some people want the B2B charger, which we sell that too, but it does creates a lot more heat”

So there ya go. BUT! He also said in a prior email that:

“We don’t recommend that you charge at a rate more than 50% of your bank capacity.   The battery will handle 100 amps (of charging) also but it will shorten the life-span of the battery.”

In our 2007 Sprinter with stock alternator, we typically see amps near the 100 amps mark into our solar batteries. Since this is well under the 50% mark of our 600 amp hour bank capacity, we are safe. If you only had a single 100 amp battery in your solar bank, that option may not be a good idea. Without further adieu, in a “Spare me the labor, just give me the baby” fashion:

My Recommendation: Isolator vs B2B (Battery to Battery) Charger

If you have a 100 amp battery bank, charge via the alternator using a sub 50-Amp B2B Charger

If you have a 200 amp battery bank, charge via the alternator using a sub 100-Amp B2B Charger. UNLESS your alternator is smaller than 140 amps, you could, in that case, use an Isolator.

If you have 300 amp hours or more in your battery bank: Choose the isolator UNLESS being able to feed your batteries a regulated amperage is important to you.

Final Thoughts & Opinions:

The B2B charger is the safest and easiest to plan for option all-around. That said, both options are perfectly good options. MANY people with 100 and 200 amp hour battery banks are using an isolator with great success (especially the 200 amp hour battery bank + isolator combo). If that’s what you want to do, go for it!

For the purpose of this website, I sometimes have to opt to recommend the safer, more reliable option. But just because I recommend one over the other, doesn’t mean I don’t think both are still fine choices.

Now that you know most of the basics of how to charge your camper van electrical system with your alternator, lets dive a little deeper into the specifics of choosing a battery isolator.  Check that out here:

Everything that you are learning here is put to use in our FREE Interactive Solar Wiring Diagrams.  If you haven’t yet, check them out as they are a complete solution for a camper van electrical system.  Check them out here:

Remember, this is just one part of a full camper van electrical educational series.  To see all of the individual guides, click here:

Finally, If you found this guide helpful, It’d truly mean the world to us if you’d share it with somebody who can use it, pin it to pinterest for later reference, or share it to a facebook group when somebody has a question about this subject.  Click the bubble in the lower right corner to subscribe to be notified of future updates and as always, leave any questions you’ve got in the comments below.