2017 Prius: Battery draining after turning on

how many miles on her?
new tyres can cause mpg drop, what model and brand?

get a fre 12 volt load test at most auto part stores. even though almost new, 12.3v is low.

sounds like the hybrid battery has a bad cell. perhaps the veepeak isn't reading all the codes

 

Getting hot enough down there to work the A/C harder? That'll drain the traction battery quicker.

 

You've got an 8 year or 100K mile warranty on that traction battery. Take it to a dealership to get it checked out - if your still within warranty.
The mpg loss is most likely caused by your new tires, but a weak traction battery will also cause this.

 

I can tell you that my experience with a weak hybrid battery sounds like your symptoms. About 4-5 mpg drop due to reduced hv battery capacity to help the engine, fast discharge resulting in an engine start (sometimes at a traffic light), all while using the ac and sometimes slow recharge on the freeway (probably because more engine power is needed to maintain speed). No hybrid battery codes ever.

Replacing the hybrid battery with new oem solved it all. Better mpg, never an engine start at a light and faster top offs on the freeway.

Normally the hv battery stays fully charged except after longer idles of 15-25 minutes with the ac on while occasionally waiting for the wife. I minimize this scenario which also causes wide engine temperature changes. (Note: Longer idle times have shorter cycles between engine on as the hybrid system only partially recharges the hv battery each time).

Again, no codes as the original hv battery was still functioning. The dealer won't be much help unless it codes.

Some believe the paid Dr Prius phone app has an accurate hv battery capacity test. I find it is too variable on the same car but it's about the easiest indicator. You do some forced high rpm charging in D with the brake on and then drain it according to instructions in an effort to test capacity.

See Dr Prius demo pics below

 

You didn't say how many miles on her, but I'm betting your model has the Nickel-Metal Hydride (NiMH) traction battery. These are the classic symptoms of NiMH losing performance based on age/miles. Only thing to do is have the battery cells tested and reconditioned.

 

The A/C is variable power, anywhere from 250 to over 2500 watts depending on how hard it needs to work, so reports of how long the battery charge holds up "with the A/C on" can be highly variable with conditions.