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Keep your car battery topped up with a solar panel trickle charger

battery solar charger

Martynn Randall is technical editor at Haynes and has been with us for 27 years. He's written more than 60 Haynes publications and has owned more than 85 cars and 60 motorbikes... so far!


Modern vehicles place a strain on their battery even when parked and locked up. They are packed with electrical systems – such as the immobiliser, convenience and engine management systems – that draw current from the battery. After only a few days in some cases, those little bits can leave you hearing the dreaded ‘click’ when you try to start the car. This is a common occurrence when you leave a vehicle in an airport car park and head off on holiday for a week or two.

If the car was parked at home, you might be able to leave it connected to a battery maintainer, but that's impossible when you have to park on the street. Luckily, there is an alternative: a solar panel that can be plugged into the vehicle's diagnostic socket (OBD).

They’re readily available, inexpensive and many come with a plug compatible with the design of diagnostic sockets fitted to all cars since about 2001. You may also be able to buy an OBD power cable separately. The solar panel pictured below is made by Ring but other trickle chargers are available (such as SCA Solar Maintenance Chargers and Powertran Solar Battery Chargers).

Ring solar charger

How does a solar car charger work?

The OBD sockets in cars all have the same terminal pin assigned, which is connected straight to the battery positive feed. So even with the ignition switched off, that pin allows direct access to the battery.

All you have to do is place the solar panel on the dashboard or attach it to one of the windows (with the sucker pads provided), then plug the cable into the diagnostic socket. 

The socket is normally under the facia on the driver's side, although this can vary, so have a look in your Haynes manual. 

That’s it! Nothing more to do. The panels don’t produce a lot of power, but it should be enough to keep the battery topped up, especially if the sun's beating down – and we're generally pretty lucky with that here in Australia. The panels also work well even when direct sunlight isn’t available and, because they are fully automatic, they will only pass charge to the battery when the output from the panel is greater than the current voltage of the battery.

It could just avoid that horrible feeling you get when you discover the battery's flat and all you want to do is get home as quickly as possible.

solar panel to charge a car battery