NOCO Genius 1 Amp battery maintainer, $30 at Amazon. You will love it.

 

Just recently measured our Es on now a 6 year old original battery after 2 weeks parked. 12.3v.

Mind you that battery is in the boot so not subjected to extreme temp or humidity.

 

Is that under load? A fully charged battery can show 13+ volts.
Regardless, 6 years is great!

 

I like the Battery Tender brand the best, I've been using mine since 1995.

 

I've already have several battery maintainers but I don't usually use them on my daily driver. My mower and muscle cars get them in late November. I got 12 years out of my last muscle car battery before it wouldn't crank after sitting a few days during the summer.

My draw is less than half of the manual's limit for parasitic draw yet it dropped to 2.2V after sitting for 12 days. It was not locked in my garage. I never lock it in my attached garage. My home office is above the garage. Close enough that if I leave my phone in my office, it connects Bluetooth and I don't notice until it starts cutting out half way down the driveway. Maybe my keys in my pocket are too close.

I usually try to drive it at least once a week but due to circumstances, it was left in the heated garage for too long. I'll be more careful again. I got complacent. It never leaves me stranded if it gets out of the garage by itself and the alternator is putting out 14.5V last time I checked it.

 

Knuckle - You may just have a battery that was simply ready to expire and needs to be replaced with a new battery. It could have a shorted cell which commonly happens to fairly new batteries that are not very old, and such a battery's voltage will drop to near zero. A battery that has its voltage drop to only 2.2 volts after attempting to charge it sounds like a battery that has an internal problem and is worthless for anything besides a boat anchor an trying to bring life back into it is fruitless.

That trickle charger on a dead battery may have confused the car's electrical system (low voltage and with a trickle output that probably turned on and off randomly with practically no amperage capacity to speak of may have been why your car reacted the way it did and the security system automatically locked the car doors. It's not a 60s Buick muscle car!

Your problem may be the battery itself and not have anything at all to so with your car. I'd get a new battery and if by-chance you do have a problem with your car draining the new battery you'll know soon enough - but in the meantime you can take the battery back to where you bought it for a replacement, and then try to tackle the problem with the car 'if' you actually you do have a problem with your car. A new battery should buy you the necessary time to see where the problem actually was (the battery), or is (the car). I'm betting the the problem is the battery itself... If I were you, I'd hope it was the battery and not the car...

 

The battery charged just fine after dropping to 2.2V for who knows how long. It scared me to see it that low but it seemed to recover when I charged it overnight at 2AMP. I removed it from the charger and hooked the battery back up to it. It started 12 hours after. I drove it 10 minutes and parked it for 4 hours and it started again with no issues. This battery is less than 2 years old. I checked the parasitic drain with the old battery that behaved the same way. It was slightly over 2 years old when I replaced it. It came with the car when I bought it.

I know I don't drive it long enough to really put a full charge on the battery as much as I did but it seems rather short regardless.

I've owned it for about 4 years and it has only done this after more than a week in the garage. It rarely, if ever, sits outside overnight unless we take it on a trip, which hasn't been a lot with COVID.