Solar Panel Car Battery Charger (Sizes/Timing + Advice)

Solar panels provide clean, limitless energy with little maintenance, making them perfect to set and forget. This opens up a lot of different uses for solar panels, including battery chargers.

Solar panel car battery chargers keep car batteries in tip-top condition, even if they aren’t used for a long time. Some solar chargers even come with extra features and can charge much more than just car batteries. 

However, if you’re specifically looking for a car charging the battery, you want to look for specific attachments and features that improve its functionality, including:

  • Charge controller
  • Reverse charge blocking diode
  • Multiple attachments
  • Sturdy construction

Solar panel car battery chargers can help improve the life of your battery and keep it ready for when you need it.

Car battery being charged and tested

Is There Such a Thing as a Solar Panel Car Battery Charger?

Short answer: yes. Solar panels can be attached to car batteries and charged them. And there are many solar chargers made for this purpose. They keep car batteries topped up on power, so they’re always ready to go.

Solar car chargers can either hook up to the battery directly or work through a cigarette lighter directly connected to the battery (if the cigarette lighter works when the car is off, it’s directly connected). 

Some come with a suction cup you can use to adhere to a windshield, either outside or inside.

Electric Vehicles

Keep in mind these solar chargers aren’t meant for electric vehicles. They don’t produce enough electricity for the car to run. The best way to charge an electric vehicle with solar power is with a solar carport.

A solar carport is a patio for your car covered in solar panels capable of charging an electric vehicle completely. The portable car chargers discussed here are for regular 12V car batteries, not for charging electric cars.

See also: What is a Solar Charger? Understand its Functionality, Benefits and Uses

When to Use Solar Car Chargers

Solar car chargers are helpful when leaving your car alone for extended periods. Car batteries leak power over time, so if not driven for more than a couple of weeks, the battery will die.

Solar chargers convert the sunlight that comes through the windshield or outside the car into electricity and uses the power to keep the batteries topped up on energy. Hence, the vehicle is always ready to drive.

They can be more convenient than regular car starting batteries, as they can be used anywhere, even if you’re far from the nearest power bank. However, most solar chargers don’t charge the battery from dead.

Car Battery Checking the voltage

How Many Solar Panels Do You Need for a Car Battery?

Typically, the smaller the panel size, the safer it is for a battery. If you use larger solar panels without charge controllers, you run the risk of overcharging the battery and possibly destroying it.

A 10w solar car charger will keep your battery topped up just fine, but if you want to have it on all the time, smaller chargers will work just as well. Even a 2.5w panel can keep a car battery at full speed.

However, the most significant drawback of these smaller panels is time. It can take six or more hours to charge a battery if it is close to dead entirely. However, smaller charges mean you won’t risk as much as larger solar panels.

If you want to charge your battery from dead to full as quickly as possible, a higher wattage panel is excellent. A 20w panel can charge a battery in as little as 4 hours, working at max efficiency. 

But if left on with no charge controller, it will overcharge and melt your battery. So if you want to use a larger panel with more than 10w, either ensure it comes with features or a charge controller that keeps the battery from getting overcharged or buy one separately.

So you only need one small panel to keep your car battery fighting fit: You just need to decide how much wattage you need.

How Long Does It Take a Solar Panel to Charge a Car Battery?

While it depends on the size of your solar panel and the weather, it shouldn’t take more than 12 hours with the smallest solar panel in winter on a cloudy day.

Most solar car chargers are high efficiency, meaning they’re good at turning sunlight into electricity. High efficiency means they produce a good amount of power, even if the weather doesn’t agree with your plans.

A larger panel on a sunny day can take as little as two hours to charge your battery fully. Ultimately, it shouldn’t take too long to have a usable battery in your car.

Trickle vs Float Chargers

Most solar panel car battery chargers aren’t for recharging a dead battery. They’re used for keeping batteries alive over long periods when they aren’t used.

If your car sits somewhere for more than two months, you’ll want a trickle charger to keep the battery from going dead. Then, when you want to drive your car again, it’s all set and ready to go.

On the other hand, float chargers do bring batteries back from the dead. If you leave the lights on in your car or the battery is otherwise drained, these chargers will fill up your battery so that you can start your vehicle.

Most solar car chargers are for a trickle charge, keeping your battery filled with power, even if it is left unused for long periods. However, some do come with float charge functionality. Just keep in mind it will take some time to use. 

How Do You Trickle Charge a Car Battery With a Solar Panel?

Trickle charging keeps your battery topped up on power, always ready to go. If your battery goes below a certain level of energy, it shortens the lifetime of your battery.

So solar chargers help extend your battery’s lifetime and keep it ready to use.

Moreover, the power generated by the solar panel is free, clean energy that is available to everyone, making it perfect for those who like to go off-grid or are fans of green energy.

Trickle charge refers to putting small amounts of power into your battery over time. With most solar car chargers, you just need to hook it up to the battery directly or through a cigarette lighter so it can feed the battery over time.

Can You Charge a Solar Battery With a Car Battery Charger?

Yes, as long as you have the correct attachments to hook it up. In theory, any solar panel can charge any battery because the panels generate electricity while the batteries store the electricity.

Just ensure it doesn’t overcharge the battery and ruin it. Moreover, you want the panel to be capable of generating enough power to charge the battery.

Most panels can charge small and medium-sized batteries, but huge batteries require a sufficient voltage to charge, so if the panels can’t produce enough voltage, the battery won’t charge.

How Do Solar Powered Car Battery Trickle Chargers Work?

The best solar car battery charger will work using a charge controller that tells it when to stop distributing power. 

  • Let’s say you have a 10w panel charging a 12V car battery.
  • The solar panel produces about 17.6V of power, and
  • since that is higher than the battery’s voltage, the battery will charge.

As the sun shines, the solar panel produces 10w every hour, converted into the battery, raising its voltage. Around 14.4V, the battery recognizes it’s complete and gets overcharged, dropping the voltage to 13.6V.

Without a charge controller, the panel continues to feed the battery electricity. Theoretically, the battery keeps dropping its voltage when it gets too high. But you still run the risk of overcharging your battery if the panel is left on.

This is when charge controllers come into play. They shut off the flow of electricity from the panel when it recognizes the battery is full, allowing them to stay hooked up to the battery without risk.

Why Is My Solar Panel Not Charging My Battery?

Tiny solar panels may not generate enough voltage to charge the battery. The power producer must produce a voltage higher than the battery itself to charge a battery successfully.

Car batteries don’t have very high voltage, meaning you don’t need large solar panels to charge them. But if your solar panel is for charging car batteries, that’s not likely the problem. It’s more likely that the problem is with loose connections or the battery’s lack of a direct link.

A common problem is that the cigarette lighter the solar panel is plugged into does not have a direct connection to the car battery. You can test this quickly by seeing if it still works when the car is off.

If it doesn’t, then it doesn’t have a direct connection to the battery, it won’t work if the car is off, and neither will any connections attached to it.

Can I Drive My Car While My 12v Solar Charger Is Plugged In?

You can, but you shouldn’t. When your car is in motion, the battery charges automatically as part of the car’s motion. If your solar battery is also plugged in, you risk overcharging the battery while on the road.

Naturally, this wouldn’t be a good thing. If your battery melts while in motion, it could ruin your entire engine, much more costly than just a ruined battery. Not to mention the panic of smoke pouring from your engine while driving down the road.

So always take your solar car charger out before driving to prevent this nightmarish scenario.

How Do You Know If a Solar Panel Is Charging a Battery?

Some solar car battery chargers come with indicators that turn green when the battery is being charged. However, some do not.

The surest way to ensure the car battery is being charged is by checking the voltage with a meter. If the battery is charging, the voltage should slowly go up.

However, it’s best to buy a charger with an indicator, especially if you use it often.

What to Look for in Solar Panel Car Battery Chargers

There are some features you want to look for when purchasing a solar panel car battery charger, such as efficiency and durability. Some features come standard, but for others, you have to read the description carefully to ensure you get what you need.


Most solar car chargers are over 20% efficient, but it’s always good to check. You’ll want a monocrystalline or thin-film solar panel that’s at least over 17% efficient to charge your car battery.

Efficiency is essential if there’s bad weather or in the winter when the panels don’t operate at their full potential. With high efficiency, they’ll still generate enough power to get your battery topped up.


While you might not think this is a big deal, you’ll think differently when looking for a place to put a bulky solar panel in your car. Whichever type of solar car charger you want, you should always factor in the size and weight.

You’ll want your solar panel to be lightweight to make it easy to use and small so you can store it away. This is where thin-film solar panels shine, as their flexibility makes them perfect for more accessible solar panels.

Reverse Charge Style Blocking Diode

This feature comes in most solar car chargers, but it’s still good to look for. It keeps the charge from the battery from flowing back into the panel when you’re not using it, like at night.

Multiple Connectors

Whichever charger you use, you want options for when you use it. Having options for hooking the panel up to your car is invaluable.

In general, you want a connector for a cigarette lighter, for directly hooking it up to the battery, and plugs you can plug in for newer models of cars.


And finally, you want to consider the materials your solar panel is made of. You’ll want something that can withstand the heat from a car, the outside weather, and just all-around sturdiness.

Most higher-end models are made of very sturdy materials and are weatherproof, making them perfect for all situations.


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Elliot has 20+ years of experience in renewable technology, from conservation to efficient living. His passion is to help others achieve independent off-grid living.

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