Had to Reset my 2010 but disconnecting battery

Check your 12V battery. There are multiple threads on this subject. Just do a search.

 

If your 12 volt battery is the original (you did not mention), it could be on its last legs. Mine did the same thing you described and I wound up replacing it. 3 to 4 years is about the average life of them and they are not that difficult to change out. If after sitting a while again, your car has the same symptoms...change the 12 volt battery. New ones range in price around $200 +or- at O'Reillys or Autozone.

 

My 2010 battery just crapped out after nearing 58k miles. I'm sure it's end of life for you as well.

Just get a digital multimeter, or if you have a prius with a nav screen there is a way to check it there. I just can't remember what it was.

 

I think you want to enter "maintenance mode". Mine does not have OEM NAV so I'm not sure how to do it. Once you are in that mode, the 12 volt battery (if good) should show anywhere from 12 to 14 volts (engine running). But because yours is the original, it might be best just to change it rather than getting stuck somewhere. I think there are 4 nuts and bolts (10mm?) to remove - pull out the 90 degree vent plastic piece from the battery and swap it out.

 

$173 includes free shipping: Optima DS46B24R Optima battery direct fit replacement for Prius 2004 + , Prius V & Plug-in Prius with Instructions

 

The life of the battery in the Gen 3 seems to be even less than the Gen 2!

 

I just ordered/received mine. $147.05 free Prime shipping. Ordered Sunday night, arrived Wednesday. Arrived well packaged with 12.85V charge.

 

Several problems here...
First, the battery will be over 12 volts any time in Ready mode, good or bad (or missing completely). Once the car is in Ready mode, the 12V system is powered by a DC-DC converter from the traction battery, which also charges the 12V battery. If the car thinks the battery needs charging, it will use a higher voltage. (So a higher voltage like 14V might actually mean your battery is *worse* than if it were ~13V.)

Second, maintenance mode isn't a great time to measure the voltage of the battery, because you're putting a load on the battery. The usual recommendations of something like "<12.2V and your battery is less than half charged" or something like that no longer applies. (Toyota says that your battery is discharged if it is at 11.5-11.9V, as checked 20 minutes after turning the car and all lights off.)

Third, it's not even accurate. I measured with maintenance mode and a multimeter simultaneously once - the Nav's maintenance mode said the battery was 11.5V, however my multimeter was reading 12.17V. That's so far off that it's just totally not useful at all for making a measurement on battery SoC; according to the manual, fully charged can be as low as 12.6V, while fully discharged can be as high as 11.9V. That's only a 0.7V spread, which is the same as the inaccuracy I measured on my car.

Get a multimeter, visit an auto parts store for a free battery test, or just replace it because it seems like it needs it - but don't rely on the maintenance mode to tell you anything useful about the battery.