Do I have a dead battery or bad alternator?

2008 Honda civic lx with 88k miles. It died randomly a week ago when parked when I was eating lunch didn't leave lights on. When id thrn the key there was a clicking sound and the lights were flashing. Not enough power to turn the radio on. Got a jump and it drove fine. No battery light on or anything. Drive home turn it off. Turn the key but not far enough to start it and it shows the battery light. Turn the key all the way and it started again and the battery light was off. Turned the car off and about 5 hours later I went back and it was dead. Dashboard lights flashing not enough power to start the car. It seems to need a jump to start then drives normal then after sitting off for awhile it dies. Problem is I drive short distances like 15 mins so I'm not really giving it the time it needs to fully charge the battery. So is it the alternator or the battery? The battery does when it sits off I'm probably not driving it enough to fully charge it but still I feel like it shouldn't lose all charge after 4 hours or so of sitting.

If your battery is almost dead and then you jump start it and it runs fine then your alternator is working. Have the battery charged and checked. At the same time have the mechanic check your charging system to find out if it is charging at its full potential. This shouldn't cost much. O"reilly auto, Autozone, Pepboy's will do this free. I suspect a weak battery.

With the engine at idle, ckeck the voltage across the battery posts. IF it's like 14.7 volts, then the alternator is working. IF it's only 12 volts, then the alternator is bad.

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