starting issue with Master Warning light and brake light on

We recently purchased a used 2006 Prius. The vehicle has approximately 74K on it now. Well the other day my wife went to leave work and pressed the power button while pressing the brake pedal, and the Master Warning Light and brake warning light both came on. The car would not allow her to shift the car so she tried to turn it off and it wouldn't do that either. After about 5 minutes she finally got the car to turn off, and when she restarted the sequence everything went back to normal and she drove home fine.

We called 2 dealers and they both seem to be confused by the symptoms, but one thought that maybe the battery was old on the transmitter. So thinking that might make sense I replaced the battery with a new one.

Well coming home again tonight the car did the exact same thing. After about 5 minutes she was able to turn the car off again, and then it started normally.

Has anyone encountered something like this with their Prius. I've owned several Toyota's in the past and when the brake warning light has gone on it was my alternator each time. Course I'm not sure if thing even has an alternator on it. Any help/guidance would be greatly apprecaited.

 

Okay I found another post kind of similar to mine and it said to check the voltage on the 12V battery. So I went into maintenance mode and when I got to the 12V battery the voltage showed 10.2V. I then proceeded to put a load on the battery and it dropped down to 9.9V. When I put the car into "Ready Mode" the voltage jumped up to 14.3V.

The second time I did it the voltage started at 12.1V and as soon as I put it under load it dropped down to 10.1V. In ready mode it spiked to 14.7V and then held steady at 14.3V.

I did the check on last time and it came in at 10.3V dropped to 9.9V under load and jumped up to 14.7V before settling back down to 14.3V in "Ready Mode".

So it looks like one of the issues is the 5-year old battery, but I wonder if there is possibly something else.