Can jumper cables be partially bad?

[kolosy]

So because I’m an idiot, I left the key in the ignition for the two weeks that I’ve been poking at the car. Turned off (position 0), but still in there. So — no surprise that the battery died. What _is_ surprising is that when I threw jumpers on it to start it from the other bimmer, it lit up (was compleyely
dead before), but wouldn’t start. Clicks, lights dim, but no turn over. Started fine before. I did hood post to hood post first, let it sit for 15-20 minutes when it didn’t start, then moved it to battery to battery. Same deal. Feels like it’s just not getting enough juice.

hence the question — can jumper cables be enough to light the lights but not enough to jump? Or is there an actual car issue here? The cable thing is weird — the only thing that would prevent enough current flowing is internal resistance, which is either a function of effective cable cross section, or corrosion on the clamps. I see neither issue.

I ordered a 2A charger/tender to try tomorrow.

[BimmerBreaker]

can jumper cables be enough to light the lights but not enough to jump?

Yes

[R Shaffner]

Several things can keep the jumper cables from passing enough current to start the car. The cables can be bad. The connections can be bad (or not good enough.) The charging car might not be producing enough voltage and current. And the old battery will be using some of that current to start charging itself.

The charging car must be running, too. I hope you know that.

The first thing I'd do is make sure the connections are good from the charging car. Turn off its lights and AC. Have someone rev the engine to 2,000 rpm or so, and then try to start your car.

[zellamay]

Yes, and poor jumper cables can be less effective than good ones. Of course the quality of the connection is important too.

[2002Z3]

Also a completely dead cell in the battery can keep you from jumping it. Been down that road many times. Old school cars would start with a jump most times, but cars from the 1990s or so on will not. If you put a volt/ohm meter on the battery and get 11.4 volts or so, the battery is toast.There are ways to de-sulphate the cells, but it is a long and not so productive process. Get a new battery. Then, check the output of the alternator if you really want to be careful. Meanwhile, buy yourself a battery tender. They are fairly cheap at Wally World and work well. I use them for my motorcycles and cars I do not drive a lot. Sometimes 8 months of downtime. Best of luck.

[bk94si]

I've had batteries that were so dead that I had to leave the jump vehicle hooked up for 20 minutes or so to allow the dead battery to have enough charge that wasn't draining so much current so that I could start the car.

[jclausen]

Get a new battery

[kolosy]

Yeah, battery is toast. Put a 2A tender on it, it’s been flashing “below 25%” for 12 hours now. I don’t see a date code, but I would occasionally have a hard time starting the car before this, probably related. I assume it was on its way out and running it down killed it.

[fignewton]

As I always say, “If it isn’t one damned thing, it’s 12 more!!”

[bk94si]

Yeah, battery is toast. Put a 2A tender on it, it’s been flashing “below 25%” for 12 hours now. I don’t see a date code, but I would occasionally have a hard time starting the car before this, probably related. I assume it was on its way out and running it down killed it.

You are probably right but I would add that a tender doesn't really do a lot of good on a dead battery. Maintains a charge but doesn't bring back from the dead too well. I've been there with the same thing, tried charging overnight and still dead in the morning but I stuck a regular charger on and it charged right up.

[kolosy]

You are probably right but I would add that a tender doesn't really do a lot of good on a dead battery. Maintains a charge but doesn't bring back from the dead too well. I've been there with the same thing, tried charging overnight and still dead in the morning but I stuck a regular charger on and it charged right up.

it’s both, and I found the date code on the old one — 2010.