How to jumpstart a car with a REALLY dead battery?

[BLINGMW]

So I stop at a rest stop today and a guy can't get his car re-started. Relays click when you turn the key, the lights work but are dim, but there's so little juice, the trunk won't open. We check some fuses and blah blah, and it could be the starter I guess, but with the trunk and dim lights I'm pretty sure it's a dead battery. From time to time they do unfortunately fail quite suddenly.

So we find some (rather crappy) jumper cables and we can't even jump it. I'm not shocked exactly, when they short internally, they just soak up current. And these cables suck. Car is auto, so no push starting.

He decided to call AAA, we started to gather other "helpers" suggesting all sorts of things, I left. But here's my question. I WANTED to try starting it without his battery in the circuit, as I'm pretty sure that would have worked. But running a modern car without a battery is pretty hard on the electronics from what I understand, though I've never tried it. And I didn't want to try something new, risking damage to his ECU and our alternator. Or, killing myself and his family. :oops: Besides, I could have been wrong, it could be that his alternator gave up 10 miles ago and these jumper cables were worse than I thought.

So has anyone tried this? A few miles down the road I realized, couldn't I have just pulled the positive terminal off his battery, connected the jumper cables (with one to his now loose cable, not the positive terminal obviously), started his car (assuming it started), then with cables all still attached, reconnected his positive cable, and disconnected the jumper cables? That way, his car would have never been without a battery as he would be sharing ours, and well, I already exposed our car to his dead ass battery, so this doesn't sound any worse from our car's perspective. And if his ran 5 minutes ago with that dead battery in the way, I guess it should now.

Thoughts? If I had a few E30s around and a super dead battery I guess I'd try it. :lol: Would kind of be nice to know as it sure sucks to be stranded by such a simple thing.

[D_Eclipse9916]

clutch jump it, or if you dont want to risk anything. Take the battery to Advance Auto and have them put it on their charger for a few hours and then come back. Technically a battery does nothing once the car is started if the alternator is supplying correct amounts of juice.

[BLINGMW]

again, no clutch. I'm kind of interested more in finding a more practical, side of the road solution. I wasn't feeling charitable enough to drive this random guy and his battery around looking for AAP or Walmart. And FWIW, once running, the battery has the quite important job of acting as a buffer and voltage regulator. I'm not even sure some cars would run without it, and some might run but the ECU would hate it. (Please all chime in on this too, I'd like to know) :dunno: Seems I've seen some track cars run without them, but I don't know how good of an idea it was.

[Evan]

yeah ive done it that way with no battery in the car and jumper cables.
ive also had the battery cables come loose while driving and the car ran fine...until i tried to start it up again :p

voltage regulators are cheap and easy, any ECU should have one on the circuit board already. (and the battery doesnt really regulate voltage anyway)

[Maengelito]

A few miles down the road I realized, couldn't I have just pulled the positive terminal off his battery, connected the jumper cables (with one to his now loose cable, not the positive terminal obviously), started his car (assuming it started), then with cables all still attached, reconnected his positive cable, and disconnected the jumper cables? That way, his car would have never been without a battery as he would be sharing ours, and well, I already exposed our car to his dead ass battery, so this doesn't sound any worse from our car's perspective. And if his ran 5 minutes ago with that dead battery in the way, I guess it should now.

I wouldn't see why that wouldn't work. If you were really worried, you could've removed your battery, connected it to his car to see if it would start and then reconnected it to yours. You could've also connected his battery in the meantime to your car to see if it would start just to see if thats what the issue is. That should atleast confirm or eliminate the battery as being the culprit for his car not starting.

[.RJ]

So I stop at a rest stop today and a guy can't get his car re-started. Relays click when you turn the key, the lights work but are dim, but there's so little juice, the trunk won't open.

Hopefully the car in question was a VW, and you set it on fire to rid him of his misery.

[BLINGMW]

You know Evan, now that you mention it, I had a battery cable corrode *cough* E30 *cough* and fall off while driving, ALMOST got home. But no damage. And yes, the protection WOULD be pretty cheap and easy for the electronics, I've just always heard its not a good idea, owners manuals caution against it, and I wonder if all manufactures design for running without the battery? :dunno:

And sure, there is a voltage regulator, so it's not like voltage regulation is completely up to the battery, but it does help. The battery will soak up spikes, excess voltage, which pretty much makes it a voltage regulator. How much it is relied on for that, I don't know. Is the voltage regulator freaking out and hot as hell without the battery there?

clutch jump it

While we're on the subject, I did have one other bit that might be useful to someone, and that's with a really dead battery, you might not even be able to roll start it. I coasted down a whole long parking lot once, plenty of speed for a good roll start, made 3 attempts, and the alternator spinning at that slow speed just wasn't enough to overcome the battery and get ~9V to the ECU. Wouldn't start. Had to walk back up the hill and get jumper cables and another car. :?