Why is my BRAND NEW car battery constantly dying?

We have a 2002 Honda Civic. Mileage is good but we were having problems with the car battery constantly dying and so we replaced the original one with a brand new one around 6 weeks ago. The new one has died on us twice so far, once was the week after we put in the new one but it was because we forgot the GPS plugged in, which our guess is that was the cause. We were able to get that issue by having a kind neighbor jump start us. The second time was only just today and this time around we had nothing plugged in or left on, so we're trying to make sense of what it is that causes a brand new battery to die and to see what the solutions may be.

You probably have a bad alternator or some wire going into your alternator is bad, and you're draining the battery. Have a mechanic check the alternator and all the connecting wires. They need to check amp/voltage levels too. The alternator powers most of the car once the battery starts the car. Not too many components rely on the battery, because the alternator is where the juice comes from. I had the same thing happen, and the mechanic told me it was a bad wire and a bad component on my alternator. I bought an after-market alternator and every thing worked fine after. But, I went through two batteries before finding out about the alternator.

Go to automotive workshop and tell them your battery current is leaking. They'll investigate it for you and usually the cause is from the interior accessories such as MP3 Players, Screens, Cameras, Sensors, Woofer & Speakers, and ANY interior/ulterior lights.

Leave your car half day in the workshop for them to manually charge the battery & make a request to check which is the leaking power source.

It wasn't the GPS. The old battery died because you have a bad alternator, and you never fixed it, so the new one is dying too.

Hi so you could have a series of faults the number one is most likely the alternator or the starter motor. The two have a lot to do with such faults with batteries. The alternator not charging the battery and the starter motor could be draining the battery when it stood so the starter solenoid could also be the cause.

I suspect it is a failing alternator.

Your car has a battery light that should be on (when running) if the alternator is failed. Since you didn't mention this we must assume that is not the issue. Measure the battery voltage (when running) should be at least 13.7 volts to be sure.
So the odds are that it is getting drained by something. So the next time immediately after you are done driving remove a battery cable. Next day reattach if success then you have a drain plain and simple ( well not so simple)
The next step is to place a current meter between the battery terminal and cable and remove fuses and disconnecting things one at a time to get the drain down to about 30ma ( your engine computer uses that much)
even an alternator can get a fault to cause this. A trunk light, vanity light in a visor, glove compartment is a possibility., not to mention some improperly wired electronic gadget.

Your description tells me that your alternator may be the original problem, not the battery, not the GPS. A faulty diode in the alternator will discharge a battery.