Low battery message after inflating tires while charging

you were using way more juice than the 12v was receiving. in the future, only use acc with the car ready, or get a 120v compressor.
the prius battery is small, and the charging system barely adequate for normal use. you should probably put a charger on the battery since it ran low enough to trigger the warning, or leave it in ready for a long time.

 

The DC-DC converter is ON while actively charging to ensure power to fans and control units charging the car. Some would say that the aux. battery is getting a charge; just because the 12VDC line is active. I don't know how the gen5 systems are programmed to respond - but I wouldn't classify it as receiving a 12VDC charge. Some people here has watched and charted those cycles and the 12VDC current varies a lot. When you pumped up the tires, did you use a cigarette lighter powered tire inflator? In other words, pull a high current off of the 12VDC line?
That's why we say, NEVER use the accessory mode and place the car into ready mode. In ready mode, ALL systems and ECUs are active, so a higher 12VDC current draw would be compensated for. The system would ramp-up 12V power on demand. Don't know if it'll do that while the traction battery is charging, because that ECU may be asleep.

You should probably get your aux. battery checked out and recharged, if needed.

Hope this helps

I find my 12VDC battery below 11.75 volts about once a year. I place it on a charger for an hour or two and it's good for another year. It has never failed to start. I believe that data point is below 10.75VDC.

 

I never use ACC. It's always better to use READY mode.

 

and you can't do that while charging, so it's an either/or situation

 

Mine goes into "Room Mode" which allows you to use power with the DC converter on.

 

that's cool!

 

I was guilty of occasionally blowing the 15 amp fuse to the lighter socket. I installed a 20 amp circuit breaker instead. I'm not worried about it in the slightest.

 

You need to use a DVM, turning-on the car also powers up the DC-DC converter; rendering your voltage measurement meaningless. Someone here was trying to say their battery was OK when measuring the 12VDC through the cigarette lighter outlet. Well on a gen4 that's on a relay that turns-off with everything else, so turning on the car will also wake up the DC-DC converter.

YMMV

 

You should get this so that you could monitor and record the 12-V-battery voltage continuously:

BM2 battery monitor on Amazon

The ON mode does not charge or float the 12-V battery. It is similar to the Accessory mode.

The READY mode turns on the DC–DC converter but does not necessarily charge the 12-V battery. It keeps it at a float voltage (13.53 V at idle or 12.89 V while driving) for most of the time. You need close to 14.0 V for charging to happen. The 12-V battery management system (BMS) has a very complicated and buggy algorithm that decides when the 12-V battery should be charged, even when the car is in the READY mode. The BMS controls the DC–DC converter voltage.

For a flooded cell, 100% SOC is about 12.64 V, and for an AGM, it is about 12.89 V.

It is interesting that the car turned off the DC–DC converter when you switched into the Accessory mode. It is on in the OFF mode during active traction-battery charging.

So, yes, you will learn a lot more if you install a battery monitor.