Extremely fast battery drain
 

Nice day today so I thought I'd put fog lights back in the front bumper with new bulbs in the BMW. Found the connectors were heavily oxidized green, cleaned those submersed in water/baking soda. Turned the car on a few times to check the bulbs (one connector was wonky) and one time it wouldn't start but then it did. Turned car off (had been leaving it "on" to listen to the radio, and buttoned everything up. Went to turn car on and it was dead. 9V at the battery went to 5V even with a Gooloo tender/charger on it. Finally pulled that off, pulled battery terminals off and put the Noco Genius 5 on it.

Driving to work this morning no issues, no dash light. When doing the lights, started right up to change wheel direction for access.

How does a battery die in 2 hours? Bad part is windows are down, sunroof is open and super smart BMW engineers decided to lock the key in the ignition when battery dies. WTF.

It seems impossible that soaking the fog light bulb connectors in baking soda. Or leaving the key on listening to the radio 2-4 10 minute periods.

How do you think this happened?

Duragold is probably 4-5 years old, no date on top so who knows. 2007 328i.

Thats a fair bit of heat.

Check amps across terminals in fuse box?

Did you reverse wires to the frog light and now positive goes to ground?

Check current drain and pull one fuse at a time to find the faulty circuit. A 5 yr old battery that has been run flat a few times may be a gonner.

Was the fog light switch in the 'ON' position when you cleaned the connectors?

Good thing for me is the H8 bulb housing only goes on one way. Going to leave it here and let it charge overnight and then start testing tomorrow.

That exactly what I may need to do but definitely don't want to do. I don't think the battery has ever gone dead. It is recharging fast with the Noco now.

Sounds like the battery is toast, Might have one shorted cell or...

I'm not super smart but even I wouldn't leave it on. :D Car was off. After the baking soda bath, dunked many times in water, let try for 10 minutes and then sprayed acetone inside the terminal ends with a lab bottle.

Is that the correct size battery for the car? BMW usually run a pretty large AGM battery for a reason. Every time the car wakes up draws a fair amount of power for about 15min. As for the key stuck in ignition, were you sitting in the car when trying to remove? Make sure the wheel is not turned and loaded against the key.

If that's the case I've got a spare battery for the Cayenne that should fit. Neither I nor a shop could figure out why the truck was starting 1 of 3 to 20 turns of the key 2 years ago so I got a new battery just in case. Turns out it was a bad starter motor that I replaced only because "while you are in there" when I did the thermostat and some other work. Pure joy since then. Turning a key typically 10 times to start gets old fast.

Yes, it's the correct battery. It's as big as the Cayenne's so if I need another, that will go it. Fluke says it's at 12.98V right now. Heading home soon so will put the battery terminals back on over night and see what I get tomorrow morning.

Wheel spins freely, not locked, but the key is in the receptacle.

It just seems strange that it would drain so fast. It was 35ºF when I left for work this morning and it started right up. And again a few times moving the car to work on it and then while fussing with the bulbs. Then dead.

With Noco disconnected got 12.69V. Started right up, 14.25V at the battery at idle.

Looking forward to tomorrow morning.

(IIRC for lead-acid)
12.6v, at rest with static charge removed with a brief load, is 100%.
12.2v same is 25% charged.
When cranking, battery load should stay above 12v and never drop below 9v. Electronics run at 5-9v depending.

Batteries usually last 3-5 years but a few have survived a decade.
5v is dead. Probably an internal short as mentioned.
Replace, or the alternator might get overloaded even though it supplies most juice while running.
Don't disconnect battery while running.
Even touching the terminal wires backwards once can kill the alternator diodes, which can cause a short and drain. Bad ju-ju.

No dash lights is an interesting tangent. There may be ground issues which contributed to premature failure.
Engine/transmission to chassis is the big one, but one of the fuse boxes might also have a corrosion problem. Could be the connection or inside the wire itself. Some look good but..

Finding a short in a circuit can be as easy as disconnecting the battery negative and putting an amp meter across the gap.
Pull fuses for radio/alarm and other known Keep-Alive-Memory devices. Be careful as some might require a code and OBD2 monitor cycles will reset to zero. There are jumpers for those.
Pull fuses until the parasitic draw goes to zero. That's the culprit circuit chain. Somewhere in there is the problem.

FWIW, Early_S_Man always said use vinegar, distilled water and alcohol in that order. I don't remember exactly what he said about dielectric grease but IDT he was against it.

I think something in your fog lights has gone to ground. Did you meter the lamps individually to see if the resistance is the same on both? Have you metered the ground side of the socket with the installed lights off and the key on? Should show continuity to known ground but no voltage. Maybe a little phantom voltage. You can always check for current but watch out for amps. over 10 will blow your meter.

Car started right up just now. going to keep a battery and tools in the trunk just in case and don't want to wait for AAA.

If a god battery drained that fast, I would be looking for melted wires somewhere.