How to trickle charge your campervan starter battery – 4 different methods

Keeping your campervan starter battery topped up isn’t just a nice-to-have, it’s essential if you want to avoid that dreaded moment when you’re ready to hit the road and your van won’t turn on. Whether you’re parked up for days in one spot or heading into colder months when batteries can drain faster, trickle charging your starter battery can help keep things running smoothly.

A trickle charger is designed to slowly replenish a battery’s charge over a long period. Unlike standard battery chargers, which deliver higher currents to restore power quickly, trickle charging provides a steady, continuous flow of electricity. This ensures the battery remains topped up whilst avoiding the risk of overcharging.

In this article, we’ll run through a few smart ways to do it – from using your MultiPlus to handy plug-in solutions, and even a couple of creative workarounds if you’re ever caught short.

Why would you want to trickle charge your starter battery?

Most people don’t use their campervan every day, and unlike your leisure batteries, the starter battery doesn’t get any love unless the engine’s running. When your van is parked up, the starter battery can be slowly drained by parasitic loads – things like GPS trackers, alarms, central locking systems, or factory electronics that quietly use power in the background. Over a few weeks, it can be enough to cause a problem.

Trickle charging keeps your starter battery gently topped up, which is especially handy if:

• Your van is in storage or parked up for extended periods
• You want peace of mind before heading off on your next trip
• You’ve had issues with a flat starter before and want a back up
• You plan on travelling somewhere remote and don’t want to be caught out

It’s one of those small tweaks that can save you a big headache, and luckily, there are a few simple ways to achieve it.

Victron MultiPlus trickle charger

Some Victron MultiPlus inverter/chargers include a built-in ‘trickle charge’ function. This is designed to send a small amount of current to your starter battery whilst the system is charging your leisure batteries. It’s a handy built-in feature that can quietly keep your starter battery topped up in the background.

Which MultiPlus models support trickle charging?

Most Victron MultiPlus and MultiPlus-II models include a small DC output for trickle charging, typically rated at 1A. It’s not enough to recharge a flat battery, but it’s perfect for maintaining a healthy charge over time, especially when your van’s parked up with solar or shore power connected.

You’ll usually find a small pair of terminals on the unit labelled “+Starter Batt” or “+Remote on” (depending on the model). These provide a regulated 13.2V output when the charger is active, specifically for maintaining the starter battery.

How to connect to the MultiPlus trickle charge port

To take advantage of the built-in trickle charge:

1. Identify the dedicated trickle output terminals on your MultiPlus.
2. Run an appropriately fused wire from this output to your starter battery positive terminal. This is usually 6mm².
3. Ensure the system ground is shared between your leisure and starter batteries, as the trickle function relies on a common ground (i.e. a non-isolated system).

So, whenever the MultiPlus is charging your leisure batteries (from solar or shore), it will also send a small trickle charge to your starter battery.

What to do if you have a different system voltage to your starter battery

If you’re running a 12V starter battery and a 24V electrical system (due to a large inverter), the output won’t work by default.

In that case, you will need a small DC-DC converter (e.g. 24V to 12V) to safely step down the voltage for your starter battery. This allows you to still make use of the MultiPlus trickle output, but without risking over voltage on your starter.

Want to include trickle charging in your campervan electrical system but don’t know where to start? Get in touch and one of our engineers can help design your system.

Ablemail AMT12-2 trickle charger

If you’re looking for a tidy, fully automatic option to keep your starter battery topped up, the Ablemail AMT12-2 trickle charger is a brilliant bit of kit. It’s designed specifically for this job, and does it in a smart, configurable way.

Unlike more DIY-style setups, Ablemail’s trickle charger is purpose-built to monitor your leisure battery voltage and only send power to your starter battery once the leisure batteries are fully charged. This means:

• No manual switching
• No risk of flattening your leisure battery
• It only passes on excess charge when there’s excess power available (e.g. once your batteries have been fully charged by solar)

It’s also compact, and simple to integrate into most 12V campervan electrical systems.

Using the Ablemail to harness excess solar power

One of the clever things about the Ablemail is how it can acts as a solar dump load. Once your leisure batteries are fully charged and sitting at a higher voltage, the unit recognises that there’s excess solar power available. Rather than letting your charge controller throttle back and waste that energy, the Ablemail automatically diverts it to your starter battery.

It’s not that the unit “talks” to your solar charger directly – it’s simply watching the voltage level of your leisure battery bank. When the voltage rises above a set threshold (indicating the batteries are full), the Ablemail switches on and begins passing current through to the starter battery.

When the sun drops, or your leisure battery voltage dips below the cut-off point, the Ablemail AMT12-2 switches itself off again. This way, it only ever uses spare energy, and never risks draining your house bank when you actually need that power.

It all comes down to voltage sensing and thresholds. That’s what makes it a great ‘fit and forget’ option: it automatically turns excess solar power into charge for your starter battery, without you needing to remember to do anything at all.

Installation process

The Ablemail is designed to work with all common battery types (lead acid or lithium) and it has a maximum current rating of 4A (though in practice, the trickle current is usually much lower). It’s also compatible with every kind of alternator setup, including Euro 5/6 engines, smart alternators, start/stop systems, and even regenerative braking.

You can fine-tune the Ablemail’s behaviour using its built-in settings. To adjust them:

1. Disconnect all cables.
2. Connect the leisure battery positive to SW1 (switch 1) and the negative to the 0V terminal.
3. Remove the SW1 cable, then reconnect it within 40 seconds.
4. The Ablemail will flash. The number of flashes corresponds to the setting you’ve selected.

Settings 1-4 are the right choice for most campervans. Settings 5-8 are better suited if your vehicle has a higher parasitic drain (for example, lots of factory electronics or a tracker that’s always active).

	Alternator	Leisure batt.	Vehicle batt.	Battery
Setting 1 / 5	Standard alternator	> 13.0V	> 12.8V	Lead acid
Setting 2 / 6	Standard alternator	> 13.5V	> 12.8V	Lithium
Setting 3 / 7	Smart alternator	> 13.5V	> 12.4V	Lithium
Setting 4 / 8	Smart alternator	> 13.0V	> 12.4V	Lead acid

This gives you a simple way to match the unit’s behaviour to your own setup, without any extra equipment or complicated programming.

When it’s the best option

The Ablemail trickle charger shines in situations where:

• You have solar charging your leisure batteries and want to use the surplus
• Your van spends a lot of time parked up (especially off-grid)
• You want a ‘fit and forget’ solution that won’t drain your leisure battery
• You’re after something that works automatically without needing to think about it

Because it only activates once your leisure batteries are full, it’s particularly well-suited for solar-rich setups where you often have excess energy sitting unused. Rather than wasting that power, it gets put to good use, keeping your starter battery healthy.

Plug-in battery charger – a handy back up plan

Sometimes, simple is best, and that’s exactly what this method is. By keeping a mains battery charger in your van (such as the Victron Blue Smart IP65 15A), you’ve got an easy back up option for charging either your starter or leisure battery if you ever get caught out.
If your starter battery is flat, just plug the charger into one of your 230V sockets inside the van if you have an inverter (or when you’re hooked up to shore power), and connect the charger directly to your starter battery. It will begin charging right away, just like at home.

It’s a particularly useful tool if:

• You don’t have a built-in way to charge your starter battery
• You want peace of mind when heading to remote places

You can also use it to top up your leisure batteries if you don’t have a shore-power charger built in. Simply connect the battery charger to your leisure batteries and plug it into the hook-up post to fully recharge your system.

If you’ve got the space, this is one of those ‘just in case’ items that can really save your trip. You might never need it, but you’ll be glad it’s there when you do.

Bonus option: Reverse-wiring your DC-DC charger (if you’re stuck!)

This definitely isn’t Plan A. But, if you’re in a pinch and need to get some charge into your starter battery, there’s a clever little trick that can help. Reverse-wiring your DC-DC charger.

Most DC-DC chargers are designed to pull power from your starter battery and charge your leisure batteries while you drive. But in an emergency, you can flip the inputs and outputs around and turn the charger into a makeshift power supply for your starter battery.

Here’s how for a model such as the Orion XS:

1. Swap the input and output wiring – connect the leisure battery side to your starter battery, and vice versa.
2. Set the charger to ‘Power Supply Mode’.
3. Double-check all your connections, and do not touch any live cables during operation.

⚠️ Important

• This isn’t how the charger is designed to be used – it’s a workaround, not a permanent solution.
• Always reverse the change as soon as you’re done – leaving it this way can damage your system or confuse your future self.
• Be extremely careful with polarities, cable sizes, and fuse ratings.
• Only do this if you’re confident working with DC systems and understand what your charger is doing.

This trick can help get your starter battery going again if you’re stranded and have no other option. It’s not pretty, but it works, and sometimes, that’s what you need!

Final thoughts

Trickle charging your starter battery might seem like a small detail, but it can make a big difference. This is especially important if your van spends long stretches parked up, or you’re heading off-grid for extended adventures. The built-in features within the Victron MultiPlus can be super handy. But on the other hand, adding a dedicated solution like the Ablemail Trickle Charger can give you more flexibility as to the functionality. Alternatively, keeping a trusty plug-in charger tucked away for emergencies is the simple option.

A well-maintained starter battery means no flat battery surprises, no early-morning jump-starts, and no trip cut short because the van won’t turn over. Just one more way to make van life a little smoother.

Whichever method you go for, it’s worth taking the time to set it up properly. And, always know your backup options in case things don’t go to plan. Because when you’re miles from anywhere, the last thing you want to hear is silence when you turn the key.