Tried to start my car this morning and nothing .(headlight switch was off),checked the battery and it read less than 1 volt(did return to 5 volts after being diconnected for a while). Drove the day before with no apparent problems or lights.
Battery is a die hard gold about a year and a half old. checked pos battery cable to ground read 1.8 ohms went up into the high k ohms when I removed the horn/stop fuse(which was good) .Also after market alarm installed.
Am I chasing gremlins or did the battery just suddenly die.
It is what it is. If you read less than 12 volts directly from the battery, the battery is considered dead. And yes, battery’s can fail in the blink of an eye. It’s happened to me!
It is possible that the brake light switch is stuck, which is making the brake lights stay on. Replace the battery and go look at the brake lights. If not, test the battery load with the car off and see if it’s sending power. Keep in mind that it should be sending a little power (keeps the ECU, radio, and clock memories up, among a few other things) but not all that much.
1.8 ohm draw with the car parked and turne off would imply over a 6 amp drain on the battery with the car turned off. That’s more than 60 watts. I can’t imagine anything drawing that amount of power when the car is parked and turned off. Some cars leave the lights on for a while after you park the car now-a-days, so that might be what you are measuring. Maybe someone here knows how to disable that “feature”. If the ‘temporary lights on’ is not the cause, then something else is wrong with the car’s electrical system; that’s what is draining the battery. First thing I’d do is carefully inspect the wiring harnesses connecting directly to the battery. Are there any frayed wires? Is the positive terminal of the battery close to any chassis component, bolt, etc, which could be grounding it out? Is the battery loose at all? Can you move it around? It should be solidly in place so it doesn’t jostle around when you are driving.
It’s true as Tester says, a battery can fail suddenly, but from what is said in the OP, I don’t think that is the problem in this case. If it isn’t an obviously observed short in the wiring harness, the first thing I’d do is completely disconnect the alarm system. Especially if it aftermarket. The technicians who install these things sometimes take shortcuts.
thanks for the advice shadowfax, stuck my head under the dash and found the plunger
on the brake pedal armature had broken off. apparently depressing the switch turns off the brake lights
