Jump Start Your Car With A Drill Battery

Sometimes, you move to a new city, and things just aren’t going your way. You’re out of cash, out of energy, and thanks to your own foolishness, your car’s battery is dead. You need to jump-start the car, but you’re feeling remarkably antisocial, and you don’t know anyone else in town you can call. What do you do?

It’s not a problem, because you’re a hacker and you have a cordless drill in the back seat of your car. The average drill of today tends to run on a nice 18 volt lithium battery pack. These packs are capable of delivering large amounts of current and can take a lot of abuse. This is where they come in handy.

Typically, when jump starting a car, another working vehicle is pulled into place, and the battery connected in parallel with the dead battery of the disabled vehicle. Ideally, the working vehicle is then started to enable its alternator to provide charge to the whole system to avoid draining its own battery. At this point, the disabled vehicle can be started and its alternator can begin to recharge its own battery. After disconnecting everything, you’re good to go.

The drill battery, delicately resting on the front bumper, with jumper leads precariously attached. The risk of a short-circuit is readily apparent here.

Being stuck in a (relatively) foreign land and not wanting to speak to anyone, I decided instead to substitute the other vehicle’s battery for my RYOBI ONE+ drill battery. This presents several challenges and risks, however. The most basic problem of all is making a connection. Most drill batteries have a very unique molded connector designed to secure them mechanically into a drill, as well as make electrical contact. Trying to connect a sizable pair of automotive jumper leads to a terminal less than a square centimeter in area is difficult.

A voltmeter makes the job easier. With the drill battery in parallel with the car battery, we see the system hit around 12 volts.

Worse, attaching jumper leads to such tiny terminals often puts the positive and negative jumper leads at risk of shorting on each other, which can create sparks or lead to a battery fire or explosion. Be exceedingly careful making the connection, particularly if you’re in a fire danger area. I was blessed with a truly petite set of leads which were close to perfect for the task. If your jumper leads are just too big, you might have some luck if you can scrounge up some metallic objects or scraps of wire to cram into the terminals to make an adapter of sorts. See what you can come up with, but be careful doing it.

The other major problem is one of voltage. Automotive electrical systems operate nominally at 12 volts; in practice the system sees anywhere from 10-15 volts in use, due to varying loads and alternator outputs. This is readily visible if your car has a voltmeter installed on the dash. Higher voltages can damage components in the car’s electrical system, particularly in newer cars and those with electronic fuel injection. So how do we get away with this? Well, in one respect, sheer dumb luck. I was well aware that my battery was very dead – the car battery was reading less than 10V on the voltmeter. This is below the point at which the battery begins to undergo sulfation, which can cause permanent damage. Knowing this, I was confident that my relatively small drill battery (with a capacity of just 2.4Ah) would likely see its voltage drop significantly when connected to a load consisting of an almost entirely drained lead acid car battery. This is much less likely to do damage than if you were to do something intentionally silly like connecting a full 18V drill battery directly to delicate components such as the ECU. If you’re having a good day, in the short-term, you’ll likely be fine. That said, take this on at your own risk, and keep in mind that some cars don’t like being jump started at all.

The final problem is one of capacity. If you’ve got a big, strong drill battery, and a small compact car, you’re fairly likely to succeed. I had a medium-sized drill battery, at 2.4 Ah, and a 1.6 L four-cylinder motor to turn over. You’re less likely to be successful trying to turn over a 6.9 L Cummins with a half-charged 1.2 Ah drill battery. You can always give it a go, though.

Revs equals success!

Well aware of the risks, I decided to press on anyway, and connected the drill battery to the car battery, ground to ground, positive to positive. It was then as simple as turning the key, and with a self-satisfied bark – my engine sprang to life! Success! I was then sure to immediately disconnect the drill battery, lest the alternator back-charge it and cause damage.

Overall, I was remarkably pleased and made it home well in time for supper. What’s more, I later threw the drill battery back on charge and it had seemingly suffered no ill effects whatsoever! Hopefully this can get you out of a tight spot one day – it’s a useful trick to have in your toolkit!

87 thoughts on “Jump Start Your Car With A Drill Battery

  1. Mikes Electric Stuff did a video on this back in 2015 as well, starting a huge truck with a Makita drill battery. I found that video fascinating (YouTube link AsTJKSH7mCU)

    1. I had a drained and partially frozen battery once when the car was sitting outside at -20…-30 C for a week, so I bought two 6 Volt lantern batteries and connected them to the battery for 15 minutes, and it accumulated enough charge to start.

      The battery was pretty much done for after that episode. I drove to the hardware store and bought a new one immediately as I got it started, and it was already dead when I came back out from the store. Same trick again, so I could drive it to a DIY shop and swap the battery out in a heated garage.

      1. Lantern batteries always seem crazy expensive in Ontario here, cheapest way to get them is wait until the lantern battery flashlight (with battery) goes on sale for $3.99 or so. Don’t suppose we’ll see much more of that now white LEDs are here. …. so in that sitch, I would have probably taken the battery out and shoved it in the oven on lowest setting 150F-180F got it nice and warm then see if it’ll play nice, meanwhile have the block heater plugged in.

  2. I would think that a somewhat safer alternative would be to allow the drill battery pack to simply charge up the lead acid battery. It will not have enough juice to bring it all the way up of course, but, it should/might be able to get it to 11 point something volts and enough to start on its own…maybe. That way, you are pumping 18 volts into the battery and not the vehicles electrical system. Just a thought. That’s what I do with my boost pack..

    1. automotive electronics are designed to take double battery voltages without failure, we routinely test at 18 volts, most companies spec require 19 volts for an hour and 24 for 10 min (in the case of something linear so it does not overheat and burn itself off the board)

      1. Very much this. In addition to that, car electronics must endure “load dump” (loose battery clamp while the alternator is charging the battery) surges which may go up to 80V for tens of milliseconds, so it comes pretty rugged right from the factory.

      2. If my memory serves right, automotive electronics have to be tolerant of up to 60 V transient spikes induced from elsewhere in the system, like from the ignition coils, starter motor back-EMF, relays clicking, etc.

        I remember reading a forum about people connecting LED strips beneath the car and complaining about blown voltage regulators, where it was suggested to put zeners etc. to protect them from the spikes.

      3. I don’t doubt what you say. Where I work, a woman’s BMW had a dead battery and I keep a jump pack by my desk to help folks when needed so I went and got it but, she called her husband who called the dealer who said do not EVER try to jump start a BMW as it will totally wipe out the electronics and both computers. So, i just let her wait there while the dealer sent a technician out who installed a new battery on the spot and then she drove home. I have been working on cars since the 1960’s and never heard of this before. At first I thought it was just a scam so the dealer could sell an overpriced battery and charge for a service call but I have since spoken to a friend of mine who is a repair technician and he said there are several brands of vehicles that can not be jump started without killing the electronics. So, anyway, that is what I was thinking of when I suggested using the battery pack to charge the other battery.

        Bill

        1. PS It would not shock me to find out that this is still just a rumor started by some car companies to sell overpriced stuff. That lady said her husband read that in her BMW owner’s manual and that had I attempted to jump it, I would have owed them new computers. Nice.

        2. This is kind of correct. If you try and jump it and the jump pack is not big enough the steering lock will stop working and need to be reset with a diagnostic tool at the dealer or auto locksmith.
          The worst problem though is people using jumper leads and connecting them incorrectly in one of many ways – destroying electronics in the process

    2. There is a really good data-sheet / app-note called something like “automotive transients” which describes all the conditions car electrics can expect, it’s well worth a read.

      Just found it – Littelfuse AN9312.5

  3. I did this one winter several years ago — Nobody else was home and I didn’t really know any of the neighbors, and especially didn’t want to wake them up on a cold winter morning! For whatever reason I didn’t happen to have any bench supplies handy, but I did have a dewalt 18V (NiCd I think, not Li) battery. Started a Toyota Echo just fine, though in my case the battery never seemed quite the same after!

    1. if it’s NiCd give it a zap with a welder or other high current high ISH voltage supply , a second or so usually does it, brings em back into service for a while. no idea how this works, saw a YouTube video and tried it on a long obsolete power tool and it worked like a champ.

      1. You can do something not entirely dissimilar for lithium phone etc batteries, where they’ve gone so low they’ll no longer even charge. A few seconds’ zap with 5V across the terminals, perhaps from a USB lead with the plug cut off, can shake them up enough that if you quickly stick them back into whichever device, it’ll wake up enough to start charging again.

        Not sure exactly which bit of protecting / charging circuit, and where, is being tickled, but it’s worked for me.

  4. I had a not completely dead battery, but not good enough to turn the engine, and started it up with an electric impact wrench on the crank bolt…Transverse engine, and the inner fender shield had a rubber plug in it right over the flywheel that popped out and allowed access, so could just get the impact in there with the wheels cranked full right. Anyway, turned the engine, a little slow then went faster and caught. Whereupon I yanked back the impact…. but the socket still stayed on the crank bolt… so had to sit and watch it run 15 mins hoping it wasn’t gonna throw the thing with the velocity of a bullet, until I was confident I could switch off, grab the socket off and it had put enough in the battery to restart it again.

    1. I owned a 69 Land Cruiser wagon (FJ-55) that had a hand crank attachment on the harmonic balancer, and a slot in the grill for the hand crank itself. I didn’t have one, but I’d love to have tried it!

      1. Apparently the trick is to keep your thumb on top in case they kick back.

        Now theoretically, you miiiight be able to do it from the damper bolt on many cars, by using a sturdy 1/2 drive ratchet and socket and kicking at it underneath the car. (Assuming you’ve got enough juice to the ECU etc on anything since 90ish) Or possibly tying a rope to the end of it and yanking it… However, for any manual or semi manual alternate cranking method, I recommend that a) you turn it over slowly a couple of times first with the ignition off, to get some oil moving and break the stiction. and b) that if it’s particularly cold try to get some warmth in the oil/block by running block heater, or putting camp stove or making small fire under the oil pan, so it turns easier.

  5. When you have that 6.9 L Cummins you’ll likely have another hefty vehicle with a hefty battery as well. We have two 5.9 L Cummins Dodges, so don’t expect to need the drill battery trick, ever.

    The devil of jump starting is in the details, of course, as we all know. Those fat cables from What-Mart, with the big copper clamps? They might hide 18-gauge wire under fat plastic insulation. The clamps are copper colored, but made of steel. You connect them up, and nothing happens until you check all the possible spots for connection failure.

    Some hacker with spare time and a bit of genuine copper could do a project on how to build good jumper cables.

    Our jumper cables are welder cable with four “don’t know where we got them” clamps made of real copper, not just plated or painted.

    1. It’s not so much of a worry if you are at the place where you store another vehicle, being stranded in the middle of nowhere is the worry for most people. Unless you’ve got to be somewhere in a time sensitive manner.

      Does the copper oxide on your clamps not affect your jumper cables?

    2. One of the perks of working in a welder repair shop was good jumper cables.

      We made our own cables for jump starting engine driven welders and generators (units as big as a mid sized sedan).

      90mm^2 flexible welding cable with welding earth clamps with big crimps squished down with a hex shaped crimp die.

      They used to work brilliantly, I just wish I made a set for myself while I worked there.

    3. I found this out the hard way, what was sold as “heavy duty copper”turned out to be copper coated steel clamps and wire with a huge amount of insulation, almost like ht leads.
      In the end I bought welding wire and four earth clamps, not cheap but extremely good.

  6. I am not surprised this works. With 2.4 AH 18V there is about 155kJ of electrical energy available. Just leave the drill battery connected for a few minutes. The charge will flow to the car battery and charge it a bit. The main starting current (~500A) will come from the main battery anyway. You can disconnect the drill battery before you try to start the car.

  7. I used to simply switch to second gear (real women don’t drive automatic) and give the car a push, jump in and start. Worked fine about 50 times or more.
    With my current car this probably don’t work. It’s all electric. Then again … talking to people really isn’t that hard and you normally don’t risk ruining any component of your equipment by doing it. Well … at least on this continent, I hear it can be different elsewhere.

    1. I value the fact that I was originally taught to drive on not one but two manual transmission trucks. It was night and day difference between the two in at just what speeds they liked to be shifted and how easy or hard it was to get them to engage. This was good because I can apply that skill to a wide variety of vehicles if I ever need to. That experience has come in handy at various wide-spread times throughout my life.

      Almost as much I value the fact that none of the cars I own are manual. That extra effort just to drive really isn’t necessary in this decade. Why bother?

      It would however be cool if automatic transmissions had a way to shift them into a special gear while not already moving that allows a push start.

      1. Curiously, 50’s-60’s GM cars with powerglide automatic transmissions could be push started. Those transmissions had two fluid pumps – one driven by engine and one by driveshaft. If you got the vehicle up to ~15mph in neutral, there would be enough fluid pressure from the driveshaft driven pump that you could shift into low and it would spin the engine to start. This was actually published in the owners manuals as a feature!

      2. >”That extra effort just to drive really isn’t necessary in this decade. Why bother?”

        When you drive stick for long enough, it becomes automatic to the point you just don’t think about it. Then it feels weird not to have it.

        And having a clutch in winter conditions is nice. First thing to do in over/understeer slide is to slam the clutch to free the wheels to match the road speed, so you get your steering back. Another thing is rocking the car out of an icy dip when the wheels get stuck.

      1. There’s a fair chance it’ll go if it lights the dash, or you just got a single turn of the engine out of it, but yah, if it’s very dead, you might not even get anything if you got someone to tow it or had a long downhill, because the ECU not powered to turn on the field coils of the alternator even.

  8. Well… that IS a hack, congrats on that!

    It’s not a hack I would recommend though except in the most dire of circumstances. Stuck in a desert with a dead car battery, a fully charged drill no water and the vultures are circling? Yes! Thank you for saving my life! Stuck with a dead car battery in the middle of civilization? Yah, I get not wanting to have to talk to strangers but some times you just got to suck it up.

    As the author said, it would be easy to accidentally short the clamps together. That would drain the battery further. Over-discharging a car battery is not good for it. Any time your battery wears down there is a chance it isn’t coming back. Draining it further makes your odds worse. You may be buying a new car battery!

    Then there is the possibility it might blow and spray you with acid. I’ve seen shorted car batteries. I haven’t seen one explode… but why tempt fate? 5 out of 6 is pretty good odds yet I don’t play Russian Roulette either!

    Then there is your drill battery. Come on, you can’t tell me it’s built for that kind of sudden draw. I’m surprised it didn’t explode! Even if it works I can’t imagine that the drill battery isn’t damaged at all. I bet it’s lifespan and/or capacity is reduced by abusing it this way.

  9. I once read a story in a computer magazine where someone started a Ford Taurus with two Macintosh portable batteries which were just just 6volt AGM batteries.batteries.
    But that said all you need is to get a charge into the main battery the battery being used to jump start doesn’t have to supply high amperage.
    You can jump start a car off flashlight batteries if you give them time to put enough charge into the car battery.

  10. My motorcycle battery effectively is a drill battery. Just a handful of LiFePO4 18650s stashed under the seat. I will never curse over lead acid again.

    Of course that little engine is easy to start with whatever energy source you have lying around, including your foot. I love a kick-start. Some day I’d love to retrofit one of those wind-up inertial starters from an old airplane and put it into a bike or car. I know a guy with a custom truck who has a badass powder charge starter, where you take basically a blank shotgun shell and fire it into an old turbocharger to wind up the crank. There’s a stock and receiver of an old double-barrel shotgun fixed into the center console next to the gear shift, so you’ve got two attempts to start before you have to reload. It’s so satisfying.

          1. I guess that makes the spark plug in the cylinder sitting on the compression stroke fire.

            I wonder if you could do that if you jimmied a way to send spark at a button mash on a more recent car.

    1. Yep, mee too but in a car, so paralleled with a string of super caps. 4S5P pack of 18650, each cell is only charged to 3.9V (float charged to 15.5V by solar panel) so very light pack but can still run the hazards all night if needed.

  11. I wonder if you could bend up a U shaped handle and weld a mount on you car to hold the drill and use the handle to spin the still and use the drill to put a charge on your battery. Some clever 3D printing you might be able to make both the male and female pieces so you could pop your drills battery in or use the drill with a crank. Also as an aside, am I the only person who has ever welded a bolt to a car scissors jack so you can run it up and down with a screw gun or 12V impact.

          1. Spitball, you’ve got around a 8 to 9″ pulley on teh motor driving a 2.5 to 3″ pulley on the alt, so 3:1 advantage, idle say 700ish so around 2000 rpm gets you there, presume you can get about 120 rpm from a hand crank so you need about 9:1 gearing, so yah, 26 to 28″ bicycle wheel I guess.

          2. You need about 1000 – 1200 RPM on the alternator before it starts to put out anything, looking at specs found on google. So if you get 120 RPM at the crank, a ratio of 10:1 is needed. I’d put a double gearing on it to make it smaller – otherwise you’ll be grinding your nose on the wheel.

        1. Probably more reliable, if you’re going to bother rigging up an old exercise bike, to just mount a separate 12V generator onto your Heath Robinson gadget, so your pedalling provides 12V without having to Frankenstein graft onto bits of your engine.

          Then again if we’ve gone to the point of dismantling bikes, you could just buy one of those battery pack things that plugs into the cigarette lighter and tops up the battery from there. Or catch the bus.

        2. Most of the time, the field assembly retains some residual magnetism – enough to boot strap the alternator. Alternators that have an integral regulator typically have a few diodes to pick off juice from the stator coils to power the regulator & field coil – separate from the main rectifiers. So all you need with these alternators is to get them spinning and a little residual magnetism.

  12. Surely usable in situation where you don’t have any other option. However, that battery has 18650 cells in 2P5S configuration and is rated for peak current of 30A and sustainable current of 15A. That’s way bellow current you need to start a car, so I’d rather use drill battery to charge car battery for some time and then disconnect drill battery and try to start car. Otherwise it’s possible to damage drill battery, and those things are not cheap.

  13. I don’t mean to be “that guy,” but I don’t believe Cummins has ever offered a 6.9L Diesel. I suppose it is possible for someone with the 6.7L to have bored it out to 6.9L. To your point, that guy probably isn’t jump starting his truck with a drill battery, though.

    1. Well don’t forget there’s those dilberts around that will advertise their truck for sale as “F-250 with 7,3 Cummins, new tunnel cover, positrack, corinthian leather seat covers, new cadillac converter….”

      1. Lol “Built-in Yeti cooler, 64 oz cupholders, and laser-etched Browning logos throughout. Retrofitted with triple HID lights with ‘mirror track’ technology that actively scans and focuses the beams onto the mirrors of the car in front of you, chief. This truck has a TRO against it and cannot be within 50′ of my kids and I cannot pick them up for visitation. You’ll be hoss of the boatramp with this bad boy…”

  14. A while back I was having problems with my car’s security system draining my battery by randomly flashing the lights. I wired an XT60 connector to the battery. When the car wouldn’t start, I’d just plug a 3S drone battery into the plug and it would start up fine. Didn’t even drain the drone battery much, so I could just leave it in the car (in a lipo safety bag), unplugged of course.

    I eventually found the pin-out for the security system’s plugs and removed the wires that activated the light flashing. This was after fooling with it several times to stop it from going off for no reason.

  15. i heard you can hold a crowbar across a cold,low battery , draw a good spark, and the battery will warm up ’nuff to bring her back to starting capacity….anyone can confirm this is true?

    1. In limited circumstances…. Though flipping your headlamps on is an alternate trick if they’re wired to the switch… mostly it’s when you’re fairly sure you battery was holding decent charges and it got hella cold, possibility of being frozen. Though usually it kind of happens in an organic fashion thus: You get in, turn key, it goes wub wub clickclickclick, you turn off key, mutter “oh shit” under you breath, turn off hvac turn off interior lights, mutter an appeal to the gods under your breath, (This has put a first high load through the battery and the warmth is seeping through waking up the chemical factory) then you turn the key again and it goes wub wub BRRRRRRRMMMMMM … so yah if you are exactly sure that this is the case you can avoid the first fail to start, maintaining bragging rights of starting your car first time every time, if you pop the hood first and tap across the terminals with a crowbar.

      1. I always gotta laugh at the people that have a garage full of junk, and have to park their car outside, in the cold, rain and snow. I wish i had a garage.
        I’d bet most starting problems are simply lead oxide buildup between the battery terminals and connectors.pull it off, wire brush them, hit them back down with the crowbar

    2. If you have a frail battery and it is freezing, the battery won’t be able to deliver cranking amps and the trick might work, but a battery in that condition is not flat to begin with, it just appears so when you try to start it. A truly discharged battery can’t magically be woken up by internal heating. You could use a tickle charger or a dash mount solar panel during the winter to the same effect

  16. Nice work! — on the hack AND the writing!

    I’m really tired of all the bs comments that are like “that’s not safe” and “that might have worked for you because you’ve got a tiny car” or whatever — but you managed to work in a lot of preemptive disclaimer-like language (and educational caveats) that were nice to see in the actual article rather than in the comments section. (I’m sure some anal retentive fuck found some way to tear you up in the comments, but whatever.)

    Anyway, well done!

  17. Good example of hacking, use what you have on hand, to get the job done. It’s not about costs or risks, whether or not you can make money of it It’s all about solving a problem (filling a need), with the tool, materials, and knowledge you have.

    Of course, many of the readers don’t carry drill batteries, since they don’t have much use for them. They do have a nice cell phone, and AAA.

    Personally, I try what I can, to get back on the road, even ask a stranger for help (some times a greater risk, than shorting a battery). I’ve gotten lucky on more than a few cars I’ve owned, with just the tools and junk I carry. I’ve never owned a “new” car, so there is a good chance something fails, try to keep a box of stuff, to handle most emergencies, since I don’t use a cell phone, belong to AAA, and not really interested in walking a mile or two, just to make a call for help, then wait until someone shows up. Done that a bunch of times too.

    1. My old Renault R10 (rear engine box) had an opening through the bumper to insert the wheel lug wrench backwards, which engaged into the crankshaft, which had a kind of one-way clutch on the pulley bolt.
      I started it that way twice in the winter with a bad battery and fully drunk. :) Pull some choke, tap the gas pedal a few times and give her a crank. It helped that I was 6’3″ and 250 lbs…

  18. starter motors are optimized to start at 12v or more 11.5 won’t do it. i have a charger that brings the voltage up to 12v after only a couple of minutes on a 10v battery. there is a lot of power still left in an 11 or 10 volt battery but the car system needs the 12 volt voltage. thats why the drill battery works. it provides the voltage kick

    1. Starting is the heaviest load a car battery is likely to see, Cheap cars are sometimes designed so that the load presented by the starter pulls down the battery to the point where the battery provides maximum power, i.e. half the no-load voltage. On such cars fans run slower, lights dim, and the radio won’t work while the starter is driving the engine. The starter should work as long as the battery can provide 6 or 7 volts while the starter is under load.
      An unloaded lead-acid battery with 11.5 volts at the terminals is already about 90% discharged and may have very low voltage when loaded by the starter.

  19. once had to fix a portable water pump for the local fire force, it was a car engine in a cage with a pull starter… guess we have really strong fire fighters around here.

  20. Left my lights on in a city parking lot. For some reason I had a battery charger along, and enough tools to remove the battery. I went looking for an outlet and found one in the vicinity of the fence along the lot. I pulled the battery, lugged it and the charger to the outlet. Ten minutes later, lugged the whole mess back to the car, reinstalled the battery and after a couple slow cranks…success.

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