Need help diagnosing. I keep waking up to a dead battery. I’ve had the battery tested and its still good. They also ran a few other tests to see if something else was draining it. Everything looks good. Twice now after I’ve jump started the car I leave it running for a few minutes and it makes a loud intermittent buzz like noise. Any help would be appreciated!
Something is draining the battery when the car is off. Does the radio stay on? Does it have an alarm? Are you leaving a cell phone or radar detector or dashcam or something plugged in all the time?
If the answer to all of that is no, then you’ll need to find the drain by pulling 1 fuse at a time and seeing which one is pulled when the drain is stopped. Once you know the fuse, you can figure out what’s on that circuit and see what’s doing something it shouldn’t.
Do you have power door locks? If so, use the power door lock master switch on the drivers door to lock the car doors as you are driving. If you hear the door locks cycling, that is where your drain is. They will cycle at random times in the middle of the night.
Did you have the charging system checked? alternator, cables, regulator?
I had a similar problem. Turned out to be the overhead light. It was supposed to turn off after a minute or so when you turned the engine off, but sometimes it stayed on. Low drain, but if I didn’t use the car for a few days, enough to kill the battery. Found this only by trial and error.
“tests to see if something else was draining it” ?? That is not an easy test, as various processors go into the sleep mode after some time. You need to monitor the battery current over a period of an hour, perhaps longer. Drain should be less than 50 mA (0.05 amp) steady state.
Once you find the problem, you will probably need a new battery. Auto batteries are damaged each time they are totally discharged. Do that a few times and the battery has only part of it’s capacity.
Have the alternator checked to see if there is excessive AC ripple voltage. It should be less than .1 volt while running the engine at around 1,500 RPM.
The loud buzzing noise you are hearing after jump-starting is a little concerning. Are you able to tell where the noise is coming from? Engine compartment, under the dash? It could be a damaged alternator. If you could narrow that down, it might provide a clue as to what is going on.
Faulty door open/closed switches, engine, trunk, and glove compartment compartment lights, those are common causes for a drained battery. Do your best to check to make sure those all go out when the car is turned off. To diagnose the problem a shop would connect an amp meter in series between the battery negative post and the negative connector. With everything off it should read 50 mA or less. It can take some time for this to happen after the engine has been turned off though, as the various computers in the car’s systems all need to go to sleep first. It’s that computer-sleep thing that’s the reason for the faulty door switch cause btw. If the computer keeps thinking the door is being opened, like if the wind is rattling the door, the computer will wake up and turn on all the time drawing electrical current, when in fact it should just be sleeping and drawing no electrical current.
One side note of caution: Jump starting modern electronic fuel injected cars can sometimes damage one or the other car’s electrical system. Suggest to avoid that if possible. If the battery is dead, the best alternative is to charge it overnight with a battery charger. The safest method to use a battery charger is to disconnect the battery ground connector first, before connecting the charger to the battery.