What do you do when your car battery dies and you don’t have a jump pack on hand? You could call AAA, or reach out to a fellow motorist to help. But, if you’re like me, and you hate talking to other people, you might prefer to solve the problem on your own. Here’s how a power drill can get you out of trouble.
Rewind back to 2016. I’d just moved to a new state to take on a an engineering role with a major automaker. I was out shopping for my new home, and when I returned to my car, I realized I’d made a mistake. I turned the key and got nothing. I’d left the lights on, and the battery was dead.
I had jumper cables, but no friends in town, and my fellow shoppers looked unfriendly and mean. I also had no road service, so I was on my own. Rustling around in the back of my Daihatsu netted me a solution, though. I found my trusty Ryobi power drill. Surely, this thing could get me going again, right?
See, here’s the thing about modern cordless drills. The vast majority of them use a small lithium-ion battery pack. Inside the drill battery, the lithium cells inside are often the same 18650 cells that you find in laptops and even some EVs like the Tesla Model S. In the case of my Ryobi drill, it had a string of five cells in series, adding up to a nominal voltage around 18 volts or so. That’s higher than a car battery, but we’ll get back to that in a minute.
I’ve always been tinkering with electronics, and I was well aware these cells could happily deliver 20 amps or more without really breaking a sweat. I suspected they could theoretically hold up to maybe ten times that in a short-duration burst, such as cranking over a small engine. All I had to do is find a way to hook it up to the car with my jumper leads.
But wait! At this point, you’re probably hearing alarm bells. We’re told that most cars use 12-volt electrical systems, and here I am talking about jump-starting with an 18 volt battery. That’s six more volts, right? Surely that’s too many!
Here’s the thing, though. Cars do run on 12-volt electrical systems, but that’s a nominal rating. We call it 12 volts, but reality is more complex. A car battery actually sits closer to 12.8 volts when it’s fully charged. Meanwhile, an alternator outputs anywhere from 13.8 to 14.4 volts in normal operation. It’s the same for my Ryobi drill battery. It’s nominally 18 volts, but it ranges up as high as 21 volts when fully charged.
The Ryobi battery did sit at a higher voltage than my little Daihatsu Feroza was built for, it’s true. But there was really only a few volts in it. I figured it was close enough that I was unlikely to damage the simple automotive-grade electronics in my early 1990s car. I also knew that when I hooked it up to the dead car battery, the Ryobi battery’s voltage would sag significantly. This is because the dead car battery was trying to charge itself back up off the Ryobi pack, and that was a significant load on the small drill battery.
The hardest part was actually hooking everything up. My jumper cables were short, so I had to carefully place the Ryobi pack on the front bumper. I then hooked up the the red jumper lead to the positive terminal of the car battery, and then wriggled its jaws on to the positive contact on the Ryobi battery. This was hard to do, as the drill battery contacts were recessed and not easy to access. I then repeated the same with the black jumper lead.
This was an incredibly delicate operation with minimal room for error. The jumper cables were just millimeters apart, and the slightest slip would have seen a nasty short circuit potentially ending in a small fire. I tried to set it up so that if the Ryobi battery fell off the bumper, the jumper cables would slide off the car battery side and hopefully fall clear.
With the batteries hooked up, I gently climbed into the cabin. I noticed the Daihatsu’s volt meter was right in the healthy range, sitting nicely above 12 volts. Even though my knowledge told me this was an okay thing to do, I was nervous.
The moment of truth had come. I feared smoke or flames, but as I turned the key to the ON position, there was none—just the usual friendly lights on the dash. I cranked the starter, and the car burst into life with precisely zero drama. Success! I quickly disconnected the drill battery to stop the alternator back-charging it at the wrong voltage, and drove on home.
I was psyched, because I was now able to drive home and I hadn’t needed to talk to any randoms for help. It might sound stupid, as I’m pretty extroverted, but people in mall carparks are generally pretty uncomfortable about random people approaching them. Plus, I’d pulled off a nifty hack and hadn’t blown up my car to do it. It’s easy to sound confident about this after the fact, but I had been sweating right up until it worked. Even better—I hadn’t killed the drill battery! I plugged it back into my drill and it ran just fine.
It’s worth noting that this worked for a very obvious reason—the difference between my drill battery and an off-the-shelf jump pack was minimal. Both pack a bunch of lithium-ion cells into a small plastic case. The only difference was mine was less convenient to hook up to a car battery, and the voltage was a touch higher. As my success proved, that wasn’t a big deal in my specific case. Indeed, four years later, I’d do the same hack with a DeWalt battery and my 1992 Mazda Miata, and it worked just as well then as it did here.
I would warn you, though, not to try this at home unless you really know what you’re doing. While my early 1990s cars were perfectly able to handle a little extra voltage, your car might not be so robust. I’d be particularly reluctant to try this on more modern vehicles with more complicated and fussier electronics. I’d steer well clear of doing it on a modern BMW, for example. In contrast, though, you could absolutely do this to a Tesla Cybertruck, as it has an advanced low-voltage electrical system designed for jumping from 12-volt, 16-volt, and 48-volt power.
In any case, I found this to be a useful technique for getting myself out of trouble. There are just a few key points to note when doing this. It’s important to take extreme care when hooking up your batteries. Drill batteries often have very small, recessed contacts that are incredibly difficult to connect with automotive jumper leads. You want to avoid short-circuiting your positive and negative leads at all costs, lest you cause a fire with the drill battery or your car battery—or both. At times, I’ve used creative solutions to hook up to a drill battery, by using bits of metal to create larger, more accessible contacts, for example.
You should also accept that you risk wrecking your drill battery in doing this. The excess current draw might over-drain your batteries to the point of failure, particularly if you have a large engine with a big starter motor. Using the largest drill battery you have will also help—bigger batteries can deliver more current. There is also another way to avoid this—you can simply hook up your drill battery to your car battery, and leave it sitting for half an hour or so without cranking the engine over. The idea is that you’re using the drill battery to effectively recharge your car battery. You then disconnect the drill battery before you try turning the engine over.
Hopefully, your car battery is always full, and you never have need to do this. However, if you’re ever stuck far from help, and you absolutely need to get some juice into your vehicle, this might just save your butt one day. It’s a good idea to keep in the back of your mind, if nothing more.
Image credits: Lewin Day
Just get one of these:
Battery Adapter Power Wheel Connector w/Wire for Ryobi One+ 18V Li-ion Battery | eBay
My first engineering class involved building a hovercraft on a strict budget. I figured my 18v drill batteries already existed in my possession, so it wouldn’t come out of our team budget. So I hooked those batteries up to our 12v computer fans. They instantly revved sky high, providing too much lifting force and turning my hovercraft into an airplane.
Huh, I thought this was going to involve loosening the belt and using the drill to turn the alternator but this is more efficient. Good thing you had that style of jumper cable leads. The big alligator teeth ones would never have worked.
A few weeks ago I had my alternator go out and limped almost all the way home by periodically pulling over and hooking up a jump box to the battery and running the start sequence repeatedly to give it some charge then driving until the gauge started to dip again. I considered just leaving the box attached while I drove but a lithium battery fire in a gasoline engine compartment seemed like a bad thing. I ended up calling my wife to get a jump a few miles from the house. It was my work truck so there were plenty of power tool batteries. If I’d heard of this hack I might have been able to make it all the way home. So thanks for the tip and I’ll be sure to check out how to hook my jumper cables to tool battery terminals.
In Canada, all you do is open the hood and stand there with your arms up and dangle the jump cables in your hand (especially in Winter). Someone will probably come to your aid. Advice: Always back into the parking spot so the battery or jump terminals are accessible under the front hood.
My 1971 tr6 had a hole in the radiator to stick a crank in it to start it
Just a caution to anyone who looks at a Ryobi 18V battery and a Craftsman 19.3V, sees they’re similar in form and voltage, then rationalizes the 1.3V difference as “nominal”. I did that just before using a 1.3v battery watching my 18V Ryobi tool go up in smoke, half a second after pulling the trigger. Turns out Ryobi has a little control board inside that appears designed specifically to disallow the use of the other brand. (I replaced that control board with a standard 12-24v PWM board and got it going again)
Did he actually say this could work to jumpstart a Cybertruck?
I was wondering the same thing.
Yes, most EVs (and all Teslas) still use a small “12V” battery. If you drain it the large traction pack won’t engage. You have to “jump” the low voltage pack with a trickle charge, and a drill pack would be great for that.
Yes – in the event its low-voltage battery is dead. The Cybertruck can accept a “jump” to its low voltage system from 12-volt, 16-volt, and 48-volt jump packs.
In this case, you’re not starting an engine. You’re just supplying the power to energize the contactors which allow the high-voltage battery and circuits to kick on.
I learned something new today. Thanks.
I haven’t tried starting a car but I have used a drill battery as a 12V power supply to test components.
I have used 12V drill batteries to power seats that need to be moved for access to the bolt while in the junkyard, ahem, I mean vehicle recycling center.
smart!
“I’d left the lights on, and the battery was dead.”
Why is it that lights don’t go out when the engine is turned off? That should be the default. If a driver wanted the lights to stay on, then they could flip a different switch.
And why has it been possible to lock the keys in the car instead of requiring the key or fob to lock the doors and trunk/hatch? (Some cars have been like this.)
I think it’s because the tow truck and locksmith mafias formed a cabal with the manufacturers.
Then there’s the double trouble of not being able to open the hood to jump the battery because you locked the key inside.
It was 2004 and a Daihatsu. They didn’t add extra logic circuitry or switches for different lighting modes. It could be a conspiracy… Or cost savings.
I was thinking of vehicles in general. Why isn’t it an industry standard that lights go off with the ignition? IIRC that’s how my old VW was. No fancy circuitry there. Just a matter of whether they run the headlight wires to a switched or unswitched pole. And I’ve had bone-simple cars that either wouldn’t let you push the inside lock with the door open, or wouldn’t even latch if you had locked it with the door open. Simple mechanical stuff.
Just be glad they didn’t use the same battery as my jag. Big enough I left the lights on overnight and it still started. Huge semi truck looking thing.
benefit of having so much space under the hood
An RC 4S Lipo battery can start a late 90s Ford Taurus. Ran speaker wire, between car battery terminals and battery (EC5 connector). Guys doing it said wire got warm quick, but it worked. The Taurus battery wasn’t totally dead, just low. No idea if the Lipo battery was still good after that as I’m not sure they would be happy with that alternator current charging it… all seemed super sketchy to me, glad none of this was my stuff, was after a local rc outdoor race.
If the voltage of the lipo is higher than the alternator’s maximum (there’s a little overlap there between some newer smart alternators and a mostly-discharged lipo, but very little) , it should be just fine. No back-feeding at all. If anything, I’d worry about it discharging too much or too fast even once the alternator’s going. Especially if the 12V starter battery’s in really bad shape.
Back on my farm worker days in the ‘70s, we had an old Ford tractor with a 6v electrical system. When it needed a jump, we just used a pickup. 12v from the truck sure spun that starter fast enough to fire the engine almost instantly. Had to be quick, since it seemed to take 10-20 seconds when the cables were connected for the battery to start boiling over.
ElectroBoom has a video about how to jumpstart a car with AA batteries. It’s easier than you might think.
I’m a contractor and drive a 2500HD silverado for work. I came out to it after a long day to find the battery dead. I was almost an hours drive from home knew noone local. I tried this. Unfortunately, I think the battery (and 6.0 gas V8) was too large in this truck. First I tried it with a larger 6ah battery and when that didn’t work I wired another one in parallel. It did try to turn over (weakly) but ultimately, no go. I’m not surprised to hear that it worked on that smaller engine. Good on you.
Lewin… I’m guessing a Daihatsu Feroza (Rocky to us muricans) is likely A: A manual, and B: Weighs about 12 lbs. Couldn’t you have just bump started it?
As someone who owns a manual that weights 12lbs and has had to jumpstart that car more than I’d like to, it’s not very hard to find yourself in a situation in which gravity or parking “geometry” really don’t leave you with much of a choice other than taking out the battery cables and hoping someone will help. Luckily where I live you just need to pop the hood and grab the cables, and someone will stop to help.
I had to jump my Toyota pickup 4×4 a few times, but my little suzuki’s were usually light enough I could manipulate them around by hand to get a good run at popping the clutch.
Theoretically, yes.
Practically, no.
I was in the middle of a crowded carpark that was mostly flat. I don’t know if you’ve ever tried to push the car yourself and then run to the door and jump inside and then perform the bump start, but it’s dangerous in an open area. The chances of me pulling that off in a busy car park without hitting someone’s car would be low.
Oh my yes, many times. Just push from the door, not from the back. I’ve had very few times where I needed to be going much faster than like… 2-4 mph to get it to turn over in 1st.
The couple of times that I rolled the car myself and jumped in to pop the clutch, I did it with no cars around me. I don’t think I’d feel safe doing it in a parking lot, even from the door (which is how I did it both times, of course).
This is amazing to me. I’ve seen 4 cylinder cars that don’t have enough juice to jump a big truck so to think that the drill battery can start a car is mind blowing to me. I’ll stick with my jump pack though
I started my air cooled Beetle with a socket wrench on the generator. Benefits of a well tuned small car.
I’ve used one of the jump packs barely larger than a hard drive to start a V8. The problem most people have with jumping cars is they use jumper cables that are too small and can’t flow enough current to start a car. That’s why I have 2 gauge jumper cables that can reach completely around a car to one behind it.
As an electrician we’ve done this at work enough that it’s what the supervisors suggest first. Usually in place of jumper cables we just strip two ends of 12/2 romex. Fits easier with modern dewalt/milwaukee batteries. And it’s as long as you need it to be! (Don’t do this)
I was thinking about my Makita tool batteries’ terminals and trying to figure out how this might be workable… You’re right, 12-gauge conventional building electrical wire is about the only thing I can think of that could wedge into the tiny contact gaps on the batteries I see on a lot of pro tools.
(A lot of batteries now use a row of terminals, about 3-4cm long and each terminal about 2-3mm wide with tall plastic barriers between each. Not friendly to any sort of alligator clips, small or large, and probably designed that way on purpose. I haven’t seen anything like Lewin’s pic since forever.)
I’ve seen people slide spade connectors into them. There are also 3D printed adapters you can make, or some you can buy online.
However, you’ll likely have none of these when you’re trying to jump start in a carpark. Which is frustrating.