Used Prius that sat for 6 months, any concerns

The big battery should be fine, the small 12 volt battery may well be dead.

 

welcome and congrats! none at all. if it's running fine and your mpg's are good, i'm sure it's in good shape. all the best!

 

That's much the same story as my 2011, which similarly "sat on the dealer's lot" for 4 mostly summer months before I bought it used, by then about 3½ years old. After I took it on a test drive with the salesman and drove it home (thereby recharging the battery a little) the original 12v, was at about 11.95 volts. Subsequent longer trips brought it back up near normal, but I replaced it 5 months later, possibly prematurely. The big battery was, as far as I know, OK.
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United States is some what vague, but unless it is mountainous there (Smokies, Rockies, Sierra, Cascades) you will not fill the big battery. The computers always try to leave some room for regenerative braking, it will take a big downhill (1000 foot drop) to fill it. Then as you level out it will go back to 6 bars as soon as it can.

 

We purchased a 2010 "new" in November 2010, with about 10 km on the odometer. It was dusty when we spotted it, at the back of a warehouse on dealer's lot. The 12 volt was completely dead, dealer replaced without quibbling.

We bought it, and it was only later I noticed from the driver's door jamb decal: build date was August 2009. So about 15 months it had sat.

Anyway, 5 1/2 years later, still champion, no problems.

 

many noobies think the battery charge indicator is telling them there's a problem, because they expect the battery to empty out and fill up. but that's not how it's programmed. it usually sits near the middle, and only at the top or bottom under exceptional conditions.

 

I agree mostly, but there are also plenty of places in the East where you can fill up the state-of-charge display. We could salvage more of that potential energy if there were a way to advise the computer to "go ahead and use up some charge, because we're about to descend a big hill." Instead, it stays stuck at its usual 6 (of its 8) segments all the way to the beginning of the descent.

 

If the battery is draining/filling rapidly, or re-calibrating, then a preventative maintenance reconditioning should be performed. Draining/filling rapidly, or re-calibrating are signs of cell imbalance that will get worse if not attended to. You can read more about this phenomenon here:
What causes hybrid batteries to degrade and fail? - Hybrid Automotive

 

how many miles on her?

 

It is very hard to recommend some one near by to United States, your location defeats real help.
if I pull into McDonalds and order, then creep around the building, the engine starts to recharge about the time I get my meal. But I run headlights 24/7 and am running A/C all year and so on and so on. it is hard to make a hard and fast rule. I can often stay in EV for a mile after coming off the highway for at least 20 miles.

 

rapidly is defined as going up and down without spending any time in the middle. you'll know it if you see it, but you won't see it at 45,000 miles. don't let your imagination run away with you.

 

Because the "traction battery" is used to propel the car, and because it is rather low capacity (6.8 A-Hrs) it will vary in charge a lot. Don't get me wrong, there's a lot of power in it, but to run the car, it takes a lot more.
It's best not to discharge it low and recharge it high a lot. Best for longevity. The HSD programmers know this, and therefore it only operates over a limited range (30% to 80% charge). You will see that as zero bars to full bars.

It's "smart", so relax and watch the blinking display.