One of the weird quirks of working from home and owning a lot of cars is that I might go a month or a few between driving a specific vehicle. This is especially true in the winter, when I just won’t drive my favorite cars at all to keep them out of the road salt. Many of my vehicles don’t have the privilege of sipping from a battery tender. Yet, when I’m ready, the cars fire up when it’s time to drive. How do my batteries stay alive no matter how long they’re stored? It’s because of our good friend, the sun!
I admit that I’m not always the greatest automotive caretaker. I usually nail fluid changes, and I try to fix big problems within a reasonable timeframe. I actually enjoy pulling a car up on my ramps and flushing out the transmission, radiator, or engine. But I do miss some things, and take too long to fix other issues. Sorry to my Plymouth Special Deluxe, I promise to get to you this spring!
The thing I was the absolute worst with was keeping batteries alive. Until recent years, if I bought a car, I could almost guarantee that I’d let the battery die. My original solution was clunky: I used to remove the batteries from my vehicles and place them on shelves in my dining room. I joked with the then-staff of Jalopnik that I had a “battery wall.” I wasn’t even exaggerating. It’s amazing my wife actually married a patently crazy person like myself.

Over time, I got battery tenders for the vehicles that get to live in my mini warehouse, my garage at home, and the garage at my parent’s house. But how do I keep the batteries topped up in cars that are parked outside here at home? I never really had to think about it until I started working from home. When I had a daily commute, I just took a different car or motorcycle every single day, and keeping batteries alive wasn’t a concern. In a way, the work-from-home life is a blessing and a curse. I can work in any clothes I want, and my commute is a walk down the hall, but I basically never leave home unless it’s for grocery shopping, appointments, or for fun.
In a weird way, I got to learn about how quickly some cars drain their batteries while others do not. My 1989 Suzuki Every, for example, can sit for a whole winter and then start right up without disconnecting the battery or using a tender. Many of my vintage motorcycles are the same way. However, all of my modern cars last maybe a few weeks to two months at the absolute most before they’re completely dead.

I scratched my head about this conundrum for a while. How do I keep a car alive that’s nowhere near an outlet? Do I just heave a giant extension cord out of my third-floor apartment and hope the condo association doesn’t get pissed? No, that wouldn’t work. What if I just installed a battery disconnect and flipped the switch after every drive? That would work, but ugh, then the clock would be wrong on the next drive.
Then, one day, I looked into the sky. Aha! What if I could harness the sun? As it turns out, it’s shockingly easy and cheap!
It’s Free Energy

I started this experiment in December 2021 when I bought this “ALLPOWERS 18V 10W Portable Solar Panel Trickle Battery Charger Maintainer” from Amazon for about $20. The test vehicle was my 2012 Volkswagen Jetta SportWagen TDI, which I had parked in outdoor storage. It was often several months or longer than a year between when I would drive this car because, due to a title issue, it wasn’t legal to drive. But I wanted to keep the battery alive.

So, I used the alligator clips included with the panel, hooked the panel up to the battery, and then put the panel on the dashboard in the car. That was it. Amazingly, the car’s battery has stayed topped up ever since, even if it was a full year between starts. Part of the reason why it took me over four years to write about this is that I kept expecting this cheap solar panel to fail on me. But, somehow, it just keeps doing its job.

In fact, here is that solar panel in that Volkswagen Jetta SportWagen TDI right before I gave it to my wife this year. Aside from some corrosion on the alligator clips, it still works! The battery itself is something like six years old, and it still performs admirably. As for the car, I wrote about the battle I eventually won in getting it a valid title. My wife has already put 2,000 miles on the car without a problem or even a check engine light to report.
A few years ago, I also did a silly test with this panel. I hooked it up to a dead lead-acid car battery and left it on my deck. It took a whole week, but it did manage to charge the battery.
Another Panel

One of the other cars I’ve been using a solar panel in is the 2007 BMW 530xi that I bought from our secret designer, the Bishop, in 2023. I do not drive this car at all in the winter. Normally, this would mean coming back to a dead battery. So, in early 2024, I decided to get another solar panel.
Since the “ALLPOWERS” one was discontinued, I went with the “Topsolar 10 Watt 12 Volt Solar Trickle Charger 10W 12V Solar Panel Car Battery Charger Portable Solar Battery Maintainer.” Gosh, I love how these silly companies name things on Amazon. Anyway, this one was also $20. I hooked it up to the battery in the back of the wagon, then hung the solar panel in the window.

This one works just as perfectly as the one that I bought in 2021. For more than the past two years, the BMW has started each and every time without issue. It doesn’t matter if the car sits all winter; it fires up without complaint. The batteries in the Volkswagen and the BMW seem to be in relatively good condition. I had concerns about overcharging, but the batteries seem to work just fine, from cold starts to power-hungry electronics.
What’s interesting is that there are debates on Reddit about whether putting solar panels under windows would be effective. I can tell you that, at least for the half-dozen cars that I’ve hooked cheap solar panels to over nearly five years, the windows didn’t stop the panels from trickle charging. The windows might reduce the panel’s effectiveness, but the panels obviously still work.
Even A Panel For Outside
So, when I bought a 2016 Mazda MX-5 ND this year, I thought that buying another solar panel was a no-brainer. The Miata has a racing battery that seemingly trades some standby time for weighing almost nothing. Personally, that’s a trade I’m willing to make because I hate how heavy typical car batteries are.

There was only one problem. I use a half-cover to protect the Miata’s convertible top, and all of my previous solar panels are neatly tucked away under windows. This time, I cooked up a slightly more elaborate solution. For $34, I picked up a “Voltset 12V Solar Battery Charger – 20W Waterproof Solar Panel Kit with Smart MPPT Controller – Trickle Charger Maintainer” from Amazon. While my previous solar panels were supposedly water-resistant, I just don’t believe that they’d survive outdoors for very long. But this one has positive reviews from folks who do use them outside, so I figured a $34 dice roll was worth it.

To install this one, I connected the ring leads to the car’s battery and then fed the line to where the hood meets the cowling ahead of the windshield. That’s where the solar panel connects to the leads under the hood. It’s nice and hidden away. The solar panel itself is secured to the Velcro arms of the half-car cover. Admittedly, I did not think this was going to be enough, but we’ve had a few high wind days and then even a thunderstorm so severe that it spawned two to four tornadoes. The solar panel didn’t budge.
The only real risk here is theft, and I can probably figure out how to lock it to the car.

As for its performance? Well, it’s been only a month, but I have no complaints. The racing battery stays fully charged. I drive the Miata only on warm days, preferably after rain washes away some road salt. Sheryl hasn’t quite aced driving manual yet, so she’s been driving her Jetta diesel wagon for now.
Something I like about this panel is that it has a charge controller that’s designed to stop sending juice to a full battery. My other panels do not do that, so it’s technically possible for them to overcharge the batteries. While I have not found any issues with my older panels, I think I will make sure all of the panels I buy in the future will have charge controllers.
But that’s it. Honestly, I couldn’t believe that the solution to my battery woes was so easy and so cheap. The best part is that, aside from the purchase price, it’s entirely free energy! The interesting thing is that, if you haven’t experimented with solar before, I think these panels could open your eyes to the usefulness of solar power. If these tiny, cheap panels do their job so well, imagine what you could do with a bunch of panels on your camper or on your house.
So, if you’re like me and you have a handful of vehicles stored outside and don’t have access to a battery tender, all isn’t lost. Instead of plugging into a wall, tap into the sun! It’s already there each and every day for most people in the world, so you may as well get some free energy from it. Your car battery and your wallet will thank you later.
[Ed note: This post contains an affiliate link, so if you buy that little charger we might get a small commision. – MH]
The post This $30 Tool Has Kept My Car Batteries Alive No Matter How Long I’ve Let Them Sit Outside appeared first on The Autopian.












