My girlfriend’s car would not start this morning - in fact everything was completely dead - dashboard lights, locks/windows, radio, etc.
A bit of poking around turned up a positive battery terminal broken in two - it looks like this, with some sort of wiring box and other cable connections cantilevered off the battery - it was broken at the thinnest center part.
My question is, what would happen if this part broke while driving (or to put it another way, could it have broken while she was driving home last night?) Would the car keep running, lights keep working, etc. with this part of the circuit broken and the battery essentially disconnected?
I think you’d be OK running on the alternator only, at least that’s the way it used to be. I’m sure there will be others who say that modern ignition systems might not act the same as back in the day. There’s never a clear answer here on these types of questions.
There is a clear answer. On a modern computer controlled car it would be ugly. The battery acts as a shock absorber in the electrical system take it out and the voltages can spike like crazy and destroy control units.
Back in the day with DC generators you could pull the battery out of the circuit and have the car run
Write this down: never ever disconnect the battery on a running car. Bad shit can result.
If the thing did break while you were driving you may or may not notice. Like Rick said there’s lots of very bad things that can happen running a modern car without a battery, but they probably won’t happen instantly.
However, IME a loose or broken battery connection almost always breaks for good when you hit the starter, not when it’s running. The small remaining connection has no problem handling the current needed to keep the car running, but when you try to run the starter motor it gets super hot and eventually melts.
The same sort of thing just happened about a week ago on my old beater truck. When I left work the truck wouldn’t start, as if it had a dead battery. Fortunately the parking lot sloped enough that I could let the truck roll and then popped the clutch to start it. I drove it home and it was fine, but when I went to start it again in the driveway to test it the truck went completely dead. I thought I had a battery problem but quickly found that the terminal had split once I opened the hood.
As long as it is making some connection, the broken battery terminal will allow enough current to flow that the battery will do most of its job as a bulk filter and voltage regulator for the car’s electrical system, and will be able to power things like the car’s engine computer and the radio and dash lights. Try to start it though and it won’t supply enough current to crank the motor, and in my case attempting to start it caused the electrical connection to completely fail and everything went dead.
It’s possible it broke at least partially while she was driving it. If so, the extra current from trying to start it would have caused it to fail completely.
If it had failed completely while she was driving it, very bad things could happen, as was already mentioned.
In the old days (like early 1970s cars and earlier) you could pull the battery wire off to test if the generator/alternator was working. If the car still ran, then it was good. Doing that test on a modern car can cause all kinds of damage to the car’s electrical system. What Rick said is worth repeating. Don’t ever do that.
No, even back in the day this was called running ‘open circuit’ and it would fry the diodes in the alternator after only a few minutes. Car electronics are so complex now I’m not sure what would happen. They probably have safety circuits/relays that will prevent damage. but they’ll also probably shut down the engine as well.
Yes, those are cheap junk. Replace both terminals with traditional ones asap. They’re not expensive.
