What Is "Normal" and What Is "Rapid" Fluctuation in Batt Levels?

I understand that rapid fluctuation in battery charge levels is a sign of a weak hybrid battery, or at least a potential sign that it might give. As I am a new Prius owner (meaning, I've only owned a Prius for three weeks, but the Prius itself is not new---it's a 2009 w/ 80K miles), I don't know what is "rapid" or what is normal.

So, would it be normal if I park the car in my garage and the battery level is one bar above the mid-point, and then after starting it 24 hours later and driving it for 10 - 15 minutes on flat or uphill surfaces, that the battery level dips to two bars below the mid-level, but then will also charge back up to one or two bars above mid-level 10-15 minutes later?

For example:
-Start the car for first time in 24 hours. Battery is at one bar above mid-point.
-Drive for five minutes, accelerating, etc. Battery falls one bar. Drive some more, take a few hills, battery falls another bar.
-Stop, turn off car, do an errand.
-Get back into car, and drive for another three or four minutes. Between braking and some downhills, battery goes up a bar.
-Drive a few more minutes, same thing.
-Home, with battery either at exact same level I left it at, OR one bar above (sometimes below).

Our battery rarely goes into the purple-colored low zone, and when it does, it charges right back to the midpoint in a matter of 10 minutes, no problem. But for the most part it stays between two bars above mid-level and two bars below mid-level, but it will definitely fluctuate within that range (in both directions) in a matter of minutes.

I have also simplified it somewhat in suggesting that the battery only falls in the first part of the journey, but only charges in the second. In reality, it will go up and down in both directions. However, I have noticed that after 24 hours, the battery will discharge more rapidly after first starting the car and driving it, and then it will charge more rapidly after the car's been "warmed up" with 10 - 15 minutes of driving.

Is this considered fairly normal fluctuation? Or is this a sign of rapid fluctuation?

I just got confirmation that our warranty was successfully transferred. It lasts until September of next year or 100K miles. (We definitely won't put 20K miles on it by then.) So I am not particularly panicked about it. In fact, my feeling is, if the battery/charging system isn't giving us really great performance, I'd just as soon as it goes sideways sooner than later (within the warranty window) so we can get a new battery on the house.

 

Thanks, Wil. I will look that product up. But I'm not still clear if my battery level fluctuation is pretty standard (actually, it seems to be the same as the other 10 used Priuses I drove), or if it sounds more "rapid' than usual.