12V battery appears dead, won't jump, then magically works

Good evening,

Thanks for all your help on this wonderful forum. I have an interesting issue with my 2017 Prius Prime (~109k miles), purchased used last year.

Two days ago, I went to wash the vehicle and sprayed the body, wheel wells, and rear trunk profusely to get grime and bugs off the exterior. I don't know if this is related, but shortly after, the following happened:

While trying to set the "delayed charging" time via the steering wheel GUI, I received a "12V battery low, set parking brake" message on the dash. Then, I received a "service traction control" and "service ABS", along with power steering warnings and a dozen other warnings I could not record because they scrolled through so fast. The car lost its center screen, dash was dim, and had all sorts of warnings going off.

Within 5 minutes, I connected a Noco GB70 jump pack and tried to charge the 12V battery. The jump pack errored out, giving the "unable to charge" message, even though the polarity was correct and the jump pack was fully charged (and known working). So I let the car sit, and drove my other vehicle to work for 2 days.

Yesterday, I purchased a genuine Toyota True Start 00544-H4470-TS battery from a local Toyota dealer. It was around $250 and appears to be the stock AGM battery.

Today, after work, I was intending to replace the battery since the car has been dead for 2 days. The last time I tried to start it with the jump pack all I got was relay clicks under the hood and barely any electronics. Now, out of the blue, the car started up, drove around the block, and everything is back to working again.

And here's the kicker - the jump pack had not been connected for over 24 hours, the car was dead as a door nail except for the warnings last time.

Should I replace the 12V battery with the one I just purchased or is this a sign of other issues? I have never owned a vehicle in 20+ years that had a "dead" battery which came back to life like this.

Thanks in advance for the help!

 

Here is the battery, if the number on the top is the date code, then it’s December 03, 2017.

 

Yes, I did press the override which allows the jump pack to “trickle charge” the battery. I don’t know if all jump packs can do this, but I’ve literally did the “force trickle charge / override button” and hooked an inverter to the clamps, and could power a small DJ speaker (it didn’t last for long, the current wasn’t there) but it DOES have the ability to “trickle charge”, just at limited amps…

Voltmeter says 11.8V when sitting but I don’t think the battery has the CCA of a new one, it appears to be 8-9 years old.