I may be under false impressions about HV Battery indicator ?

how many miles on her?

the indicator is purple when it has 2 bars, blue up to 6 bars, and green at 7 and 8.
generally speaking, it hovers at 4-6, but can go high or low depending on conditions.
the important thing is that it doesn't rapidly fluctuate top to bottom, that indicates a dying hybrid battery.
driving style has nothing to do with it, you can't damage the battery, and you can't drive in a way that would be good for it. it's designed to be driven.

 

anything is possible at 12 years and 123k, but unless you see the fluctuating i mention above, or get a dash light, you're fine.
mpg's are your best indicator of a problem.

 

if it's any comfort, our neighbor is still driving our old 2004, with around 150k, no issues whatsoever. that year was built like a tank. all the best!

 

The software does not allow the battery to go below 20% or above 80% so what your seeing is not really accurate as far as the true
capacity of the battery. The 80% is so just like you said not to consistently overcharge the battery and heat the pack up. When you see full green take advantage of it and use Electric Vehicle mode as best you can. Will quickly burn that green up.

But your car is now 12 years old and hybrid battery will soon show its age. If your concerned about the Hybrid battery health I would buy a Hybrid battery charger as you can restore the battery health and extend it for a few more years. That charger does extend the capacity of the battery to full charge which is a very good thing to do to the battery once in a while under controlled temp conditions. The charger includes a fan harness that force's on the battery fan so it does not do exactly what you surmise which is overheating the battery pack.
They sell the charger on this site its "Hybrid Automotive".

 

In winter we see Green quite often as cabin heat causes engine to run more.
In summer we see mostly blue as the air cond sucks up power
I hate purple but see that going up mountains or when A/C is on sometimes

 

Normal is 40%, not 20%, though I have seen dips to 38% during a rapid fall-off.

I second the HA charger recommendation, but I would get the reconditioning kit. That allows you to discharge and effectively "recondition" the battery in the car. Check the "Quantitative" link in my signature.

For me normal operation is 6 blue bars with the occasional 7 green and 5 blue. A/C use can force you into the 2 purple bar zone if the ICE is off (long sit in a drive-thru). Allowing the A/C to run in auto at a reasonable set temp (75-78°F) in recirc mode with normal driving is in the 5-6 blue bar region.

 

when i was commuting 7 miles to work in my '08, i always arrived with full green bars. no idea why, and it's the only drive i could replicate it consistently.