I put a new battery in. I was told that if I disconnect one of the battery
cables while the car is running and the car turns off that means it's the
alternator, so I tried that but it did not turn off. That's all I know to
There's still "mechanics" telling people to pull the cable while it's running?
They must sell a lot of electrical parts, as that's an excellent way to
destroy the alternator, the ECU (computer), the radio, and many other
electrical parts, due to the huge voltage spike caused by the "load" of
the battery suddenly being removed.
Also, if the battery happens to be charging at the time, it will be producing
hydrogen gas, which vents out the top of the battery, usually right next to
the terminals. A spark from the cable, and kaboom... a face full of acid.
Don't disconnect battery while engine's running; it could fry something in a
modern car. Get a plug-in voltmeter to keep a running check on system voltage.
The voltage should stay in the 13.5V~14.5V range when engine is running. A fully
charged battery is 12.7 volts (after 3 hours off-charge).
if the battery's fully charged after shutdown, and drops to say 12.2V overnight,
there's a drain which can be caused by a stuck switch (hood, trunk, glove box,
etc.), a defective battery that won't hold a charge, or the alternator has a
defective diode, allowing reverse current flow after shutdown.
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