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]
I’ve had a reasonably sized solar panel and a solar charge controller down below on my sailboat for 15 years now, works just fine.
Batteries are the same as car batteries, so same principle.
There was one time, where the made in China solar charger shorted out, so all the unregulated volts from the solar panel (I guess around 20) went right down in the battery. Made it explode (yup, total battery rupture with plastic fragments everywhere), and it wasn’t fun mopping up battery acid. But that was one time in 15 years, so I still see it as an overall success..
Thinking off doing the same om my VW Eurovan. But that should be for charging the leisure battery (when I get one…)
On the cars I have battery off switches, so not even the smallest amount of current is drawn from the batteries. Usually makes car batteries hold up fine for many years that way.
Well, this would work in a place where winter doesn’t bring snow, frost (that panel won’t do much behind a frozen windshield) but does have a lot of sun.
They work fine in the UK, and we can go a month without direct sunlight during the winter. These things only need to produce enough power to offset whatever parasitic draws that your car has, which is probably less than 1W.
I had a 2006 Audi A3 that had typical mid aughts Audi electrical issues. I put one of those solar trickle chargers and it did the trick, even with an all season cover on it. If the car got a lot of snow and plus the car cover wasn’t enough, but that was only a handful of times in the depths of winter. Normally, it was good.
When I first bought one of these panels it was rated at 14w.
I tested it at maximum power sun during summer at 2500′ elevation and I never got more than 10w. It’s fine but I never trust Amazon crap at face value.
Its been working 3 years and I love that it plugs into the cigarette lighter.
I don’t think solar panels ever get their full rated wattage. Maybe if you hit a perfectly clear day at the perfect latitude right at noon, but otherwise there’s going to some loss of efficiency.
I long ago learned the secondary benefit of smart chargers/maintainers for modern vehicles that are either a) not driven daily or b) mostly used for short trips – the battery will have a MUCH longer lifespan. Flooded LA and AGM batteries – unlike lithium types – like to be fully charged all the time. My last 2 batteries (2 different vehicles) lasted 8 and 10 years respectively because they were kept fully charged. These cheap solar chargers mean that you can do that even if you don’t have a garage. Highly recommend.
This is the kind of commerce story with affiliate links only the Autopian does well–recommending items the staff has actually been using, rather than whichever brand paid most or sorting Amazon results by average review score.
This is 100% something I need, so thanks for the recs!
I haven’t started truck truck in 3 weeks, I’m worried. This is a good idea.
Before I actually ran an extension cord for power to my shed I used a battery buddy solar panel to keep my motorcycle’s battery topped off, worked great until it didn’t, the weather got to it as I had it basically mounted on top of the shed. The inside the car option you’re using is a great idea.
I looked into a solar panel for a car that I have that’s parked in a second floor garage that’s half-open on two sides. There is some light in the morning, but that’s about it. It’s probably better than not doing anything, as the car can sit for a month between use (on my third battery in six years). The panels I looked at didn’t have any overcharge circuitry, so this one is a lot better for the price.
It would work better if I could trade with my neighbor, as his car is directly in the sun (the previous tenant put a cardboard cover on his front tire to protect it from the sun).
Seems like a cool ideal, although I’d be nervous to try it with my Prius v. The battery is fairly small and inside the cabin, to say nothing of fears about what overcharging might do if it’s connected to the rest of the car’s electronics and the traction battery in one way or another.
Luckily, not particularly relevant for me since I own checks notes one vehicle.
I had one of these decades ago when I had my 94 and 97 Jettas AND it was VW branded. One panel, 4 suction cups and a plug to the lighter socket. Volkswagen part number 1CO 915 687. You can still find them on eBay and whatnot.
This is such a simple thing that I hadn’t thought of for my son’s $400 Subaru winter beater. It came with a functional battery, but it has a small drain on it if you don’t drive it for more then a week. I’ve been using a household charger, but the extension cord is a pain when you need to snowblow the driveway.
Also, I completely missed that you bought an ND Miata!
Welcome to the Miata family Mercedes! You should go to the 30th annual Miatas at the Gap this summer. I want to go, but Maine is quite a ways away. We’re on our second NC Miata here and my son wants another one.
I’ve just bought an NC, and ten minutes into driving it home, I passed another MX-5, and got a wave. Miata/MX-5 people really are friendly 🙂
Yes, I’ve found that to be true as well. The online communities are also helpful. I’ve been looking at getting another one, since mine is set up a bit more towards track days. It’s still great to daily drive though.
I always wonder why, instead of those stupid glass roofs, automakers don’t just put solar panels on the roofs.
For a wagon or SUV, the roof can easily be 2m x 3m. You can probably get close to 1kW on a sunny day.
If we leave the car in an open parking lot for 8 hours, that’s enough for 20-30 miles of driving.
It can’t quite replace plugging in, but 20-30 miles of free driving ain’t nothing.
I’d be happy if my car had a solar roof and didn’t contribute anything to useable range, but just used all available solar power to either heat or cool the car as much as possible. On a hot sunny summer day I don’t need it to make it 68 degrees, but making it 90 instead of 120 inside would be pretty neat.
I always figured it was a money thing, but maybe it’s a crash test/safety thing?
The Hyundai Sonata Hybrid could be optioned with a solar panel roof. In practice the energy generated is about an order of magnitude less than you’re estimating. An extra 2-4 miles a day isn’t much when you have to pay a few thousand dollars extra for the panel.
Unfortunately, this. If you run the numbers, realistically a built in solar panel for range extension will only just barely pay for itself over the entire lifetime of the car, not to mention any losses due to the extra weight or potential maintenance issues. Cars just aren’t big enough to fit enough panel area and are rarely positioned optimally. That said, there is an argument for a smaller panel for 12v battery maintenance, as shown here, and for little stuff like running a vent fan while parked in the sun.
i do something similar, but more complex…because of course its more complex. I have a 100 watt solar panel on my roof rack full time that feeds into a solar charge controller, so whenever I’m outside I’m topping up, which is good because with the fridge in the back it actually draws a fair amount. when I’m at home and parked inside I run a second harbor freight 100 watt panel into a port in the grill I added that parallels the panels. Since the inside one is effectively off, its just the outside one doing the work. If I park in the driveway and hook up both I get a nice quick charge.
Bonus – if my battery is low, I can add any dc voltage source greater than 15v to charge it. i.e. a drill battery. It’s saved me a few times.
What is the device that let’s you input any random DC current to charge your battery and where did you buy it?
any solar charge controller. Any dc voltage in the range will charge the battery. This is the one I got. Its okay. https://www.amazon.com/LensunSolar-Waterproof-10A-Controller-Black/dp/B0CNP16NWW?th=1
I Also have one of these that does the same thing, but is meant to be inline and portable. https://www.amazon.com/SUNER-POWER-Controller-Regulator-Lead-Acid/dp/B0F9KS9JHX/ref=pd_ci_mcx_di_int_sccai_cn_d_sccl_2_6/140-3818881-0409335?pd_rd_w=c7KMO&content-id=amzn1.sym.751acc83-5c05-42d0-a15e-303622651e1e&pf_rd_p=751acc83-5c05-42d0-a15e-303622651e1e&pf_rd_r=JVYATR165796BE5KBZ7R&pd_rd_wg=5PTQ8&pd_rd_r=55518a69-6c41-4b2c-a974-2529a9a9bbde&pd_rd_i=B0F9KS9JHX&th=1
I’ve used these for years. They do the job. I got one for $8 once off Amazon or Walmart and its even held up fine. I typically just throw them on the dash. I was a bit worried about using the cigarette lighter to feed power back but it seems to work most of the time on older vehicles. I have a beater truck I silconed one to the hood because the paint was gone anyway. Getting them dirty seems to effect them more then being inside normal at least normal 20+ year old uv tent.
Important Question:
Are these compatible with my Fuel Shark™?
My gas bill went down 100% when I put a Fuelshark in my EV.
Checkmate.
I assume you pull the panel for the Miata while you’re taking off the cover, but for the cars that the panel is inside do you bother undoing the leads? Seems like the “safe” option, but maybe somewhat annoying.
For the VW, I had a lead going into the cabin. I just disconnected the panel at the end of the lead. The wire was still there, but I didn’t care. Since the panel is in the back of the BMW, it’s super easily ignored. I’ve also used the panels in Smarts, and sort of just stuff the wire in the gap between the dash and the windshield. Disconnect and reconnect for drives.
Makes sense, thanks! I have a garage and don’t need this for this application, but it’s nice to see they’re working reliably and hassle-free. I’ll probably pick one or two up just to have on hand.
I totally need to get one of these and I don’t know why I haven’t yet.
I bought a fold out solar panel from Harbor Freight years ago and did a similar set up on a sailboat. I like that you can fold it up and put it away when you don’t need it.
I switched my motorcycles to Lithium Iron and they never die, sitting all winter. They’re expensive, but so is a new battery every spring. . .
At one point I convinced myself that a fresh Yuasa every two years was worth it. But they started to give me issues in year-two, forcing me to ask for a boost on the way home from the office a few times.
If I buy the cheapest chinesium battery off Amazon, I can get reliably one year out of it. And then recycle it in the spring with a fresh one.
Annoyingly, it’s cheaper to do this assuming the Lithium one lasts ~10 years.
If feels so incredible wasteful, but at least batteries metals are mostly recycled.
Glad/not glad I’m not the only one who seemed to have issues with year two of owning a Yuasa. I also ended up just buying a cheap battery off of Amazon annually, which always felt wasteful even though I also recycled them.
I have a couple of Noco lithium motorcycle batteries, and they’re amazing. The bikes start stronger, have brighter lights, and the batteries last through the whole winter.
Haven’t really found an affordable lithium car battery though.
It perhaps stretches the definition of “affordable” (though I found a seller on eBay that had them listed for just a bit more than an equivalent Optima Yellow top) and I wouldn’t put it in something with 10,000 watt stereo or a luxury car; but I bought an Antigravity ATX30 for my Elise 5 months ago and it’s been great. Instant starts, takes up far less space (in the Elise it’s in the trunk) and it weighed something like 30 pounds less than the one that was in there.
Would probably work a treat for your Miata or your Beat.
I really like the idea of this. My project car is hopefully going to be road worthy again soon and I plan on a similar lightweight battery, but fear it will die on me one day after I drive to work, leaving me stranded over an hour away from home. I have a good trickle charger in my garage but this could be hooked up after I park at work or on a road trip to keep it topped off.
I always wondered about how you juggle so many cars! At one point I had about 4 driveable cars and that was almost too much to maintain (on top of a couple project cars at any given time). These days I have just the daily and the project car and it’s definitely much less mental load but it’s also not as fun since I don’t get the variety and excitement.
I need to get one of these for the LX, poor thing always need s a jump or a trickle charge. Finally sprung for a new battery last spring, and I’ve already killed it like three times.
I used to kill a battery every winter in my summer car. Thankfully, NAPA always replaced it every spring under warranty. I think I did that like four years in a row. I probably had a parasitic leak somewhere from a mod, but since they replaced it I never bothered to get a trickle charger or track the issue down.
Not in my hood. That thing would be gone in 5 minutes.
That’s brilliant but what surprises me the most is how cheap they are. I thought you were going to say $50-$75 but $20 is a steal.
Now if they could make a bigger EV one…
The cheapness is what has always stopped me from trying one out. I figured they just couldn’t possibly work reliably.
That’s sort of why it took me nearly five years to write about this. I kept expecting the panels to break, but they just keep working.
I think I should just snag one – it can always come in handy. I really just didn’t think it would work.
In my campervan I used a Solar + DC-DC charger that would float charge my starter battery from the solar when the house battery was topped off (so 200 watts of solar keeping everything nice and happy all winter).
I got the same charger now that I’m building my bus, but someone online mentioned it won’t work when using lithium house batteries instead of lead acid (which makes sense when there are different voltages needed for different chemistries). In which case one of these would take care of it for me.
There’s just not much that can go wrong on them. The panel itself is solid state, unless you snap it it’s going to keep working for decades (although slowly losing efficiency). I’d expect the biggest problem would be wires eventually breaking where they’re attached just from being moved every time you use the car
My dad actually has a Volkswagen one. Used to use it for his Cabrio before he built a garage.
Are you my son?
…nnnno?