[rdgrimes]

I wouldn't be so quick to look for a problem.
Its completely normal.
For starters, each bar on the battery meter represents a range of charge - approximately 10%. But keep in mind that 8 bars is 80% SOC, and 2 bars (the minimum) is about 40%. However it only takes a fraction of 1% change in SOC to flip the meter up or down one bar. Simply booting up the systems causes a drain.
Its all pretty random and you need to stop obsessing over it. As long as the meter stays between 3 and 8 bars you are running optimally.

 

[rdgrimes]

In all the 20+ years that Toyota has built these hybrid systems, not once has there been any real issues with battery management. Not one, nada, zero, zilch. That's millions of units sold and running. There's also no such thing as a system problem that doesn't produce error codes.

The battery is maintained between 80% and 40% SOC at all times. Period. I think some folks are really freaked out by the complex hybrid system and scared that its going to bite them. Fords do that, Toyotas don't. In fact its one of the most (if not the most) reliable systems ever built.

I'll add that I've always suspected there's a default "auto discharge" built into the system that allows the NiMH battery to be run down to 40% periodically as a "deep cycle" event. Its possible this could be getting done more often when its new.