Using power tool batteries to jump start cars

[Perd Hapley]

So this is a thing?

[dogmush]

It is a thing, but it's not a great idea.

Tool batteries aren't really designed for that kind of discharge, and the cheap ones that I've seen just use a resistor to get the voltage down to the 14-15VDC range.  So likely to get hot.

I guess if your battery is at the level that it almost starts, but not quite, you could use a tool bettery to give it a couple Ah charge and maybe get moving.

[Mk-211]

Stupid people, use the buzz box welder that you have in the corner! 😁

[MechAg94]

It is a thing, but it's not a great idea.

Tool batteries aren't really designed for that kind of discharge, and the cheap ones that I've seen just use a resistor to get the voltage down to the 14-15VDC range.  So likely to get hot.

I guess if your battery is at the level that it almost starts, but not quite, you could use a tool bettery to give it a couple Ah charge and maybe get moving.

I have an old Sears plug in battery charger in my garage.  I have used it to help get a start before on a weak battery.  I figured the battery was not completely dead. 

I haven't shopped for the portable starter kits lately.  They were around $100 last time I looked. 

[Boomhauer]

No it’s not a thing that is smart

[Bogie]

Cheapest jump starters are around $90 for a decent one. If you can go a little heavier, you can get a lithium battery version that'll fit under a seat for about $125 or so... I have a $200 version that is an absolute beast... Can also charge phones, etc...

[Bogie]

You could probably rig something that you could attach multiple tool batteries too, with a cap or something, for jump starting, but given the time and materials involved...
 
Or just drive by your local parts store, get the battery tested. If it flunks the load test, it is on the way out, so do a new one... Parts store batteries are generally fairly decent, but if you can find one with the same bci number (and make sure it is not a reverse), Home Depot or Menards seem to be the leaders. Don't get a Neverstart from Wally World.
 
Is your truck one or two batteries?

[Kingcreek]

I’ve seen the YooToobs do it but I wouldn’t.

On the other hand, I know a guy that took an old 14v Dewalt drill/driver and wired it with cables to run off his 12v truck battery for fencing chores.
(The 14v system is outdated and a rechargeable battery costs more than a new 18-20v tool that comes with a battery.)

Now that I think about it, I still have an old 14v worklight. I might wire it to connect to my 12v boat battery.

[230RN]

May I offer the stupid suggestion that it's more a matter of getting the car's computer up back into an operating voltage range for a few brief moments than providing starting motor energy?

Nah, come on Terry,  What the hell's the matter with you?

Nothing. My mother had me tested. This is borne of actual practice.  You can "ohm it out" all you want, it still works.

And remember, turning off the ignition on a modern car does not drop the battery drain to zero. 

Terry, 230RN

[Bogie]

Remember - it ain't the volts. It's the amps. You can have a battery showing 12 volts, but it ain't got the oomph... Yeah, you can call that 150 pound dude with the really fast 40 a linebacker, but when he has to hit that guy who weighs in at 300, that won't be pretty.

[Bogie]

Oh yeah - some parts stores sell lightweight jumper cables.
 
If you're trying to jump a car with a really dead battery, and your vehicle is strong enough, you can make those things start smoking or even catch fire.
 
If you want a GOOD set of jumper cables, get a pair of the clamps at the parts store, then go to a welding supply outfit, and buy two lengths of nice big thick welding cable. Get about 20-25' each side, and you won't have to worry that your buddy (was gonna say ol' lady, but why be all sexist...) parked nose-in where  you can't get to things. Get the biggest thickness you can afford. And don't loan them out to anyone who isn't family.

[dogmush]

If you want a GOOD set of jumper cables, get a pair of the clamps at the parts store, then go to a welding supply outfit, and buy two lengths of nice big thick welding cable. Get about 20-25' each side, and you won't have to worry that your buddy (was gonna say ol' lady, but why be all sexist...) parked nose-in where  you can't get to things. Get the biggest thickness you can afford. And don't loan them out to anyone who isn't family.

For what 50ft of good 3/0 welding cable will run you, you can buy a *really* nice set of jumper cables, and not have to assemble it yourself.  Or a decent set of jumper cables, AND a good lithium battery booster.

[griz]

Cheapest jump starters are around $90 for a decent one. If you can go a little heavier, you can get a lithium battery version that'll fit under a seat for about $125 or so... I have a $200 version that is an absolute beast... Can also charge phones, etc...

Got one last year sometime and it's proven to be a real workhorse.  Mine's "medium" size (rated for V-8 but not diesels) and is good for two or three jumps on one charge.  The USB port is also handy because my wife doesn't believe her phone needs charging until after it shuts off, and that can be at awkward times.

[Kingcreek]

I bought a box of tool stuff on an auction for $5. It it was some clamps, wrenches, junk, and a brand new still in the package from 40-50 years ago, 16’ jumper cables made in USA with welding g cable and good copper-plated clamps.
I’ve thought about portable jump packs but never bought one. I have a Schumacher shop charger with jump setting. A portable would be handy but I’ve never had a situation I couldn’t manage with what I already have.

[Hawkmoon]

I've had an inexpensive Everstart jumper box from Walmart that I have had for so long I've replaced the internal battery once, and that was a few years ago. It has served me well, but it was never a very strong boost. About two years ago I went to O'Reilly's and treated myself to a more powerful jumper/booster box. I think that is the one I bought:

https://www.oreillyauto.com/detail/c/super-start/battery---accessories/battery-jump-starters/f1ed73b0a83b/super-start-750-amp-jump-starter/ss02/55750?q=battery+jump+starters&pos=0

It's a lead-acid battery, not lithium ion, so the thing is heavy and it won't fit in the glove box or center console. But on a cold winter morning, it has the oomph to crank over a cold engine.

[230RN]

Remember - it ain't the volts. It's the amps. You can have a battery showing 12 volts, but it ain't got the oomph... Yeah, you can call that 150 pound dude with the really fast 40 a linebacker, but when he has to hit that guy who weighs in at 300, that won't be pretty.

Apparently the tool battery's voltage allows the computer to come alive in order to allow the depleted (not empty) car battery to crank the starter, albeit not as enthusiastically as a full battery.

[dogmush]

The tool battery's voltage allowsthe computer to connect the depleted (not empty) battery to the starter.

That's not how a CANbus start circuit works.  If the depleted (not empty) car battery has the voltage to close the solenoid,  it'll power up the PCM and CANbus.

You aren't really running into computer issues unless you get under 9VDC or so.
Something like a Dewalt 20V max battery (a real one, not a fake Amazon one) will probably hit 35-40 Amp (briefly)  and just start the car.  That's why Boom and I said it was a bad idea: the battery will do it, but has the real potential to get pretty dang hot, pretty dang fast.

For comparison the really power hungry tools the battery is designed for(grinders, chainsaws) are probably in the mid to high 20s amp range under normal usage.

[dogmush]

Probably worth mentioning here that both the tool and the battery have current and thermal limiting stuff built into them.

I'm not a cordless tool engineer,  so other than knowing they are present in both pieces, I can't tell you exactly which component does what. But just hooking up the batter to a car with one of those -$30 adapters from China almost certainly skips at least some of it.

[Bogie]

This is the one I have - the only thing I don't like about it is that the cables don't unplug for storage... But I won't lose the cables...
 
https://www.oreillyauto.com/detail/c/schumacher-electric/battery---accessories/battery-jump-starters/f1ed73b0a83b/schumacher-2000-amp-jump-starter/shu0/sl1612?q=battery+jump+starters&pos=1
 
The biggest cables the O'R sells are these - they're adequate for starting a real truck, but if you can do something heavier (if you occasionally need to do something really heavy duty, tractors, etc..., by all means go for the heavier gauge...
 
https://www.oreillyauto.com/detail/c/bayco/battery---accessories/battery-booster-jumper-cables/0e145bb1ea03/bayco-1-gauge-25-foot-battery-booster-cable/bac0/sl3010?pos=7

[Bogie]

And... If your car is supposed to run on 13.5 volts or so, that's what you should give it... I've seen folks get creative, and that magic smoke smells like money...

[230RN]

I still think it's mainly a matter of getting the computer into an operating voltage range (however briefly) so it can do its thing about turning functions on and off and general control.and allowing the solenoid to operate in the first place.

As I mentioned, you can "ohm it out" all you want, but that's the main issue.

I thought the "operating voltage" for the computer was 10 volts below which it shuts down completely, but dogmush mentioned 9.4 volts. So if the computer is now "awakened" and can get the starter solenoid to make contact at that low a voltage, the starter will turn over if the Cubes aren't too great, and start the engine.  I don't think creating a big enough ignition spark would be an issue.  Once a cylinder or two fire, the alternator takes over and off you go.

(One thing you might try before all this rigamarole is to  stick a Phillips head screwdriver point into the gaps between the battery posts and the battery clamps and give it a sharp rap to deform the metal a bit to make good contact. Two or three deformations per battery post might do the trick if the Great God Coulomb smileth down upon thou pooreth mortaleth.)

Terry, 230RN

[Bogie]

Cranking voltage/amperage is a thing, and the alternator won't initially run it for cranking... You have to make the computer happy, and have enough to crank the engine past the piston compression. 10 volts, or even 9.4 will work with small cars, but that's iffy to start with, and not for long. And it needs enough amps, which is why sticking a multimeter on it only goes so far - you have to check if it will keep up with the amperage required.

[dogmush]

I still think it's mainly a matter of getting the computer into an operating voltage range (however briefly) so it can do its thing about turning functions on and off and general control.and allowing the solenoid to operate in the first place.

As I mentioned, you can "ohm it out" all you want, but that's the main issue.

I thought the "operating voltage" for the computer was 10 volts below which it shuts down completely, but dogmush mentioned 9.4 volts. So if the computer is now "awakened" and can get the starter solenoid to make contact at that low a voltage, the starter will turn over if the Cubes aren't too great, and start the engine.  I don't think creating a big enough ignition spark would be an issue.  Once a cylinder or two fire, the alternator takes over and off you go.

(One thing you might try before all this rigamarole is to  stick a Phillips head screwdriver point into the gaps between the battery posts and the battery clamps and give it a sharp rap to deform the metal a bit to make good contact. Two or three deformations per battery post might do the trick if the Great God Coulomb smileth down upon thou pooreth mortaleth.)

Terry, 230RN

No.  That's not how it works.

[Boomhauer]

I still think it's mainly a matter of getting the computer into an operating voltage range (however briefly) so it can do its thing about turning functions on and off and general control.and allowing the solenoid to operate in the first place.

As I mentioned, you can "ohm it out" all you want, but that's the main issue.

I thought the "operating voltage" for the computer was 10 volts below which it shuts down completely, but dogmush mentioned 9.4 volts. So if the computer is now "awakened" and can get the starter solenoid to make contact at that low a voltage, the starter will turn over if the Cubes aren't too great, and start the engine.  I don't think creating a big enough ignition spark would be an issue.  Once a cylinder or two fire, the alternator takes over and off you go.

(One thing you might try before all this rigamarole is to  stick a Phillips head screwdriver point into the gaps between the battery posts and the battery clamps and give it a sharp rap to deform the metal a bit to make good contact. Two or three deformations per battery post might do the trick if the Great God Coulomb smileth down upon thou pooreth mortaleth.)

Terry, 230RN

You have to have sufficient amperage to turn the starter over. That’s a fact whether it’s a little 4 cylinder 2 liter engine or a 32 liter diesel.

Insufficient amperage and your starter will not turn over. Keep holding that switch while it tries and you’ll burn the starter up as well.

[zxcvbob]

No.  That's not how it works.

He got the make sure the battery cable clamps are making good contact part right.  I've done the upset-it-with-a-screwdriver thing before when a clamp was slightly loose and I didn't have a wrench to do it right.  (the battery was okay, the connection what the problem)