Prius (2004-09) :: 2005 - ABS - Power Steering Gone - Battery Dead?

If this has been posted before feel free to remove. I searched everywhere and didn't see exactly what I experienced with our Prius when the 12v battery was in it's final stages of death so I wanted to share.

Below issues all occurred within a one week time period 3-7-16 to 3-14-16. 2005 Prius with 145k miles, replaced traction battery on 7-30-15 / 127k miles.

First occurrence - happened a few seconds after starting and driving the vehicle. The ABS light came on and the power steering faded out and then came back, just briefly, and the car did not die. Turned the car off and back on again and all was well.

I performed the 12v battery test by entering maintenance mode. (hold the display button and turn the lights on/off three times, vehicle signal check, battery check) the battery was reading 11.9volts with the car off, I drove the car and it was charging at around 14.7volts and then was reading 12.2 with the car off after driving it. Which at the time seemed a little weak but nothing that was a red flag. I've read that you're supposed to replace the 12 volt battery every 4 years but I swear the one I removed looked stock.

Second time - again happened just a few seconds after starting the car and driving. ABS light came on, red triangle of death light, brake light, power steering was gone, and the power steering light came on, the car did not die. Restart fixed the issues again.

Third time - Happened about 30 minutes in to the trip while the wife was driving on the interstate around 75mph, wipers were on due to rain but visibly lost power, radio came on and off, all the lights on the dash (warning lights included) flickered on and off, power steering was gone, car died completely and would not restart. Tow driver had to boost the battery long enough to put the car in neutral so we could load it on to the tow truck. When we got the car home the battery was completely dead again.

I ordered an Optima Battery 8171-767 (DS46B24R) YellowTop Prius Battery from Amazon which appears to be a direct replacement, and simple to install. I drove the car for a few miles, returned to the house, performed battery test again via maintenance mode and the battery was charging at 14.0 and reading 12.5 when off. I can't be certain but I think the battery check feature may be displaying false information if the battery has dead cells and the car is trying to charge the battery? I took the old battery to Advanced Auto Parts and had them run a diagnostic check and the tester stated that the battery had dead cells and needed to be replaced. I gave them the old battery even though I didn't buy the new one from them and got a 10.00 store credit, unexpected and nice.