I was curious about how the 12V battery gets charged. I read that it is charged with the regenerative breaking by turning one of the motors into a generator that charges the hv battery. In turn, the hv battery charges the 12v battery. I measured the 12v battery after a trip with the RX in park and in ev mode. It appeared to be charging. It measured 13.69v. When I turned the RX off, it measures 12.18v. I did not expect it to be charging while in park, in ev mode. Is the hv battery always charging the 12v battery even when not moving?

 

When you hit the stop/start button to shut down the vehicle, the 12 volt battery is no longer charged. it would only be charged when the vehicle is on.

 

Yes, the battery sits at 12v with the car off. I got that. I was just surprised to see it charging while parked in ev mode. The hv battery must be charging the 12v even while idle.

 

Revived an older thread. I think my 12v battery was depleted.

i was in accessory mode earlier for maybe about 10 mins and the car displayed some parking brake error in the dashboard. After a few seconds I started to get other warning lights. Maybe something weird going on so I decided to turn the car off and then back on. The car refused to start and had the same error messages. After a while the electronics stopped working and the headlights started to flicker. I had to exit the vehicle by pulling the door handle twice. The door wouldn’t open again electronically. To be on the safe side I removed the physical key and pop the cap off the driver door handle to manually and ensures the door was unlocked and then I manually pulled the lever on the bottom of the handle to open the door and pop the hood open.

I’m surprised the battery died this quickly. We drove the car about 2 weeks ago and it was fine. I guess the headlights and taillights drained a lot of battery while in ACC mode (car is parked in the garage).

Currently I got a battery charger hooked up under the hood. The charger says the 12v battery is low but it doesn’t show me the precise level. I’ll let it charge overnight and hopefully the battery will be charged tomorrow. If it doesn’t charge under the hood, I might buy something like a Nico boost jumper to jump start the car.

TLDR - 12v battery died while in ACC mode. Now trying to charge with a battery charger overnight from the engine bay instead of the battery in the trunk. May invest in a booster jumping product just in case.

 

As I understandit, if on and in park, then the hv battery will supply a charge to the 12v battery, and the engine will cut in to charge the hv battery if it drops to a sufficiently low level. As a consequence, you can sit and idle in park for as long as you like, without flattening either battery, at least until you run out of petrol. Only works while on and in park though; put it in neutral and the 12v battery wont be getting charged. Similarly, accessory mode will drain the 12v battery without having the ability to charge it. So don't run electrics in either neutral or accessory mode as the 12v battery isn't big enough to run them for any length of time.

 

I just verified, using Dr Prius, that the 12v battery is charged while in neutral.

The high voltage battery does not charge when in neutral or reverse though, only in park or in a forward driving gear.

 

My RX battery died after 9 months. I do not see any 12V monitor on the instrument cluster or on the main screen. It would be nice to know if your battery is charging without opening the hood.

 

Perhaps one of those inexpensive USB charge ports with a voltage display would ease your anxiety?

 

I use Dr Prius in an Android phone with an OBDLink MX OBD2 port reader. A different port reader is needed for Apple phones.

A voltage guage such as Carbuff2 linked to would be an easier and cheaper solution if that's the only information you are interested in.

 

Yes, that was my error. The traction battery will still charge the 12v battery in neutral, and it's the traction battery that isn't being charged.

 

Thanks for the replies. I just was surprised that all of the non Luxury cars that I have own had atleast an idiot light. I will check the current draw with the car off and if it's fine, I will assume I just had a bad battery.