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Q: Car won't start after having radio playing

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While parked, waiting on a friend, I was listening to the radio with the engine was off. All electrical systems were working but my car wouldn't start. Naturally, we had to jump the car. I did some testing and left the radio on and once again, the car wouldn't start. The volt meter reads 12.8 when the engine is off, and then rises to 14.9 when I start the car, so that would mean the alternator isn't the problem. I went ahead and purchased a new battery, but the voltage reads even lower than my current battery. Can you explain what's going on?

A: When you buy a new battery, it has been sit...

When you buy a new battery, it has been sitting on the shelf for who knows how long and may start with a lower voltage.

When you start the vehicle and test the battery while the engine is running, you should be getting around the 14.5 volt range. Now turn your headlights on high beam and turn on the A/C to high blower speeds and the radio to on. Now check to see what the battery is getting. While holding the engine speed to about 1500 RPMs, you should have more than 13.2 to 13.5 volts getting to the battery.

If the voltage is below this, then you may have a problem with the alternator not putting enough power out to keep the battery charged.

If it is okay then let it idle and check the voltage and see how much the volts drop at idle. It may go to about 12.8 volts with everything on. This is normal when everything is on.

Now turn off the headlights and look at the volts, turn down A/C blower to low and check the volts. Now the volts will go up to above 13.5.

A mobile mechanic, such as one from YourMechanic can run similar tests of your battery and charging system for you at your home or office.

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