Car dies when i plug something into the cigarette lighter

I have an 02 530i. Ran and drove fine. Turned the car off one day, next day. Crank no start. Sat for a few months cuz i didnt have time to troubleshoot. Just swapped a new battery in today, and changed the fuel pump relay. Started up but died right after, but after a few starts, now it idles fine.

My issue is that now when i plug anything into the cigarette lighter, there is power to the device (air compressor). But when i turn it on to inflate the tire, the car dies almost immediately. When i unplug the device, the car starts right up and idles.

Any ideas? Thanks!

I would try to charge the battery, then test the alternator using a multimeter with the engine off, then again on, and a third time with engine still on plus headlights, radio, and can fan on blast. Look up the expected voltages and consider whether you can rebuild it or have a mechanic do so.

check you alternator is supplying correct voltage monitor for a while to see if fluctuating up or down. although you have already put a new battery in over voltage could have fried it. are other electrical components operating correctly?

Now i cant even get it to actually start. The battery died since the other day. It was a brand new battery. Tried jumping it and it cranks no start

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KevinC wrote

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Awesome, thank you. I will pull the alternator and have it tested. And charge the battery (it died sitting for those couple of days, i think the hazards were on the whole time. Didnt notice cuz its under a cover)