12 V. battery drain issues on 2016 prius

if you hit the park button, the car is still 'ready'. that means the engine, hybrid battery and inverter are all working together to keep the 12v charged.
here's what to do:
1) go to an auto parts store foe a free 12v load test, to see if it is healthy.
2) charge it up or replace as necessary
3) with the car off, measure the draw on the 12v to see if it is within spec. if it isn't, you're gonna be spending a lot of time learning how to chase down electrical goblins.
if it is, then you're just not driving enough, and you should keep it on a 12v maintainer when not in use.
4) or you could just keep it on a maintainer and avoid the hassle

 

Newer cars with keyless entry and start buttons will drain a battery. It's always scanning; look for your FOB. A few weeks without driving or recharging that small old battery will mean a dead car. The Prius in particular will run readiness diagnostics at certain intervals; powered by the 12V battery ONLY!

Get the 12V battery load tested to see if it needs replacement.

Good Luck..

 

Your protracted downtimes are very detrimental to the battery.

that’s good. It’ll likely need a replacement battery though; the current one likely too far gone.

 

I press the park button most of the time, but it only requires the start stop button to be pressed to turn off the car. I often sit for a few minutes in park watching my battery monitor charge level for the 12 volt.
If 12 volt is too low like 70% or under I put a battery charger on the 12 v. without a battery monitor it's flying blind. Amazon has them, like Ancel BM200 for $24.

 

I rarely if ever push the Park button, due to convenience of it happening in conjunction with hitting the Power button (shutting off).

that said, more times than I care to admit, I’ve JUST about exited the car, still in Ready (fully on), and in D (drive), just held by parking brake.

I think the old-school key-in ignition and conventional shifter were light years ahead in this regard.