Bad car battery ??

Could be the battery, but if it's doing nothing, nothing, then starting it might be the starter solenoid going bad.

I'm at work, but will when I go home tonight. How much should it drop?

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Put the multimeter on it and read it, then have someone crank with leads still attached...how much does it drop?

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Not a bad test simply turning on the lights 12.4 while the car is off is a good test as well.

I agree with the others that you likely have too much corrosion on one of your battery terminals. This can prevent your starter from getting enough power to turn the crank.

I would also advise having your battery tested at a local auto parts store to truly see if you have a battery issue.

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I put the voltmeter on the battery last night, and it read 12.4 V. THen I started it, and it was running about 13.8 V.

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This is normal. The battery is mainly there to crank the engine and once it's started the alternator provides electrical power. You will have a slightly higher reading once the car is running.

If your battery tests good and the car continues to die after it sits, your alternator likely isn't keeping the battery charged when the vehicle is running. Then you would need a new alternator.

I would recommend a load tester.

LINK

if its nothing then it starts its not getting a connection to the battery so 9 out of 10 times it the battery connections are dirty
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