Nosier than usual funny battery issue

Hey gang having some really weird things happen and as usual happening at the worst time. I have taken a trip out to see my grandchildren in Stafford VA. which is a 1650 mile round trip affair in my parents 2007 Prius. I drive a 2002, my wife drives a 2008, my sons is 2006 and then my parents have this 2007 which I'm having problems with. On our way out here the usual clicking that you hear under the hood ( from the magnets in the generator) got louder and louder almost to the point of concern then as we were heading back home tonight the second half of the 1650 mile trip the noise is now concerning and the car is down on power according to the seat of the pants and the MFD. The MFD showed 1 purple bar so we turn around on the interstate head back to my sons place, in that 10 miles the noise is really ticking, the next moment we have all green bars and by the time we pulled in back into the subdivision down to 1 purple bar then as I turn it off had 3 blue bars. I have plenty of experience with Prius so I can positively say we barely made it back to my son's place as it was really really low on power. It has one of those newpriusbatteries batteries in it that is 3 going on 4 years old, up until this point has never gave us a bit of trouble(except the combo meter and AC evap coil) and the car has 289,000 miles. According to my Xtool D7 scantool there are no codes, the HV battery has 15.75 volts with all cells within .02 of each other and the internal resistance of all cells is .022 ohms. I guess I'm just wanting to know if this is just a hiccup or since I have this scantool available what I should check for as I just don't want to breakdown on the interstate since I have 825 miles to go. Thanks in advance for any insight, thought or opinions and most of all thanks for this forum as you guys are the best.

 

IDK if I'm just tired or can't proof read when i miss spelling in the title my bad