Possible 12 volt battery going bad

It's a continuous float. Why they didn't implement a real 3-stage charging algorithm is a mystery, it would greatly help the life of the 12v battery.

I've slept in the Prius overnight in a hot climate (90 degrees) and left the system ready with the A/C on. It seemed like it was starting about once every 20 minutes and running for about 2 minutes. It starts off with a relatively high SOC then gets down to just a couple of bars and then the time between runs is shorter, and it really doesn't charge much. I suspect it's trying to prevent you from cycling the battery too much.

I suspect you could run it for quite some time with the A/C and all accessories off. It would probably then go to a much longer interval. It would be interesting to test!

Yes, you could turn the car on, and take the fob and leave. The car will apparently stay in ready mode indefinitely. (At least until it runs out of gas and the batteries die) But, yes, anyone could come get in the car and drive off.

It should be possible to make a little embedded system that occasionally starts the car (like once a week) with a little work. Probably not much of a market for it though unless you build it into something else that has a wider market.

 

It's about every 30 minutes with everything off and runs for just 2 minutes. Car in ready mode, pulled the P CON MTR fuse so that there was no transmission shifting, Emergy brake on, dash lights lowest setting, display off, fob in my pocket, lock doors. walked away. Seatbelt light makes it look like an alarm light was blinking.

 

Nice trick disconnecting the Parking Actuator. Another good one would be to disconnect the brake signal so the car will not shift in the first place.