Longer Idle at startup or "How long is normal?"

Advice or observations, please. So I've owned my 2011 for 6 yrs and I've put 98K miles on it (141 K total) and it's always run great with great mpg. After sitting overnight it never used to idle after going into ready mode. (Unless of course it was cold out and had temp control on.) That's slowly changed. Probably a yr or so ago it would briefly turn on and then off but now it will idle for about a minute before shutting down. (And to be clear the SOC is usually 50-60% so it's not at the 40% when it usually turns on) So fearing the battery was going bad I got an OBDII and did the Dr. Prius tests. Passed both with no codes or problems and was pleasantly surprised with the 3 life expectancy tests - 75, 75, and 77%. But I did notice one of the 14 packs is consistently lower than the rest while in battery monitor mode so I'm assuming that's why it's idling: to get them sufficiently balanced. Or is the idling possibly something else?

Not sure what to do. I'd like to keep it another 3-5 yrs but am not sure of the best strategy going forward. Some of the options I've seen are a replacement pack or cell around $50, the Prolong system at $700, a reconditioned $1600, or even possibly the new Lithium replacement $1900 out now or soon. Any other options? Or should I just leave well enough alone and the longer initial idling is nothing to worry about? Hmmm...

 

Just checked. When not driving it's bounces between .02 and .08. When driving it's all over the place but I think .56 was about the highest I saw during hard acceleration.

 

I have not. Nor have I changed the plugs or the other preventative maintenance I've seen in the NutzAboutBolts videos. (Besides the transaxle fluid which I changed at 60K) I need to do all those things and your message is a good reminder/incentive.