2022 CX-9 Battery goes dead, then resurrects...

[Yoram]

Hello all and Happy New Year!

Weird thing happened to us on New Year's Eve.
We pulled in at our friends' house, turned the engine off and were exiting as it kept beeping and showing "Ignition On".
I tried to turn it off by pressing on the starter button without pressing on the brake but it wouldn't respond.
At this point I can't recall whether we were able to switch if off or whether I attempted to start it and try to turn it off again - I suspect not.
When we got back a couple hours later there were various seatbelt and other warning lights on. Tried to start the car but it wouldn't and over the next minute or two everything went dead - not a single light on.
We got a ride home and just to launch the elimination process I replaced the batteries in both keys.
Came back to the car the next morning (yesterday) and first thing tried to start it (nothing) and then checked the car battery voltage. It read 3.9V....
I hooked it up with jumpers to my other car and after a few minutes and tries it started and ran fine with no residual warning lights.
Drove it home (about 10 miles) and parked in the garage. Today tried to start it and it started fine. Tried to replicate the previous scenario of "Ignition On" but no problem - I was able to turn it off every time and restart successfully every time.
I then plugged in my generic (Autel) OBD II scanner and there were no codes stored.
The nagging thought is whether or when this will happen again...
Anyone experienced anything similar, and any clues and fixes to what happened here?

My next step is to call the dealer and see if the car and battery are still under warranty before I surrender it and my life savings to the service department...

Cheers!

 

[Mazdiod2]

Yep, sounds like aliens, alright. Did you notice any unusual time changes, or bright lights?

A 2022 is around 3 years old now, probably all of the batteries are the originals, except for the remotes. If you ran the battery down to 3.9v maybe you should put a charger on it. I use one (from amozone) that also "desulfates" the aging battery plates. It definitely helps to keep a battery fully charged vs. run-down, which causes the sulfation.

 

[Yoram]

It is usually driven every day. I do plug our cars to trickle chargers when they are not going to be driven for a week or more. It drained from nominal 12V (when it was running) straight to 3.9V within hours or minutes, so in my mind there would have been some kind of "traumatic" event rather than simple aging. Of course the battery may be faulty. Usually a battery should last 6-7 years in normal use.
Hence I'm baffled...
Update: Car and battery confirmed still under OEM warranty and I have an appointment at the dealer to run diagnostics. Will keep y'all posted.

 

[youri]

Most likely your car stayed on and ran the battery down. But after being boosted and driven a bit then it had enough charges to restart the car and act normally.

I also recommend you charge it now to bring it to a good charge level since it is likely still low. But once charged it will likely be fine for a while.

I did the same thing than you on my 2018. Battery was fine after for another 4 years.

 

[Yoram]

Yes, I hear you, @Mazdiod2 and @youri . I did hook the car up tonight to my "intelligent" charger. It showed 77% charge upon hook-up so you were right, it definitely needs a charge. Thanks for the good advice!
What baffles me though is the root cause for what started the whole episode. Upon pressing the start/stop button on arrival, with the transmission in park and my foot on the brake, the engine switched off but the ignition stayed on and could not be turned off, apparently until the battery reached deep discharge.
Now, from what I know, modern cars do not cook their coil(s) or run their battery down with the ignition left on with a stationary engine. The engine ECM is supposed to switch the ignition off after X seconds or minutes at 0 RPM.
I have no idea what happened here and my "consumer grade" OBD II scanner does not see any faults. I hope the dealer locates the root cause and fixes it (under warranty of course).

Cheers!

 

[Yoram]

Charged the car overnight at moderate rate. This morning it showed 100% charge at 13.3V.
Will be monitoring the voltage on a near daily basis and report here anything of interest.
The car is driven daily and is scheduled at the dealer in 2 weeks (our time constraints) so by then I will have a bit of a picture also for them.