2003 Prius, acceleration issues (whining ICE), low miles, maintenance info?

So, we have a company Prius, bought way back when it was new to town and the hot-thing-to-get. It gets us from A to B when we need to go somewhere

Of course that also means it doesn't get a lot of everyday use. It's sitting at just (almost) 40k miles now, and seems to have some very sparse maintenance records... just check-ups at the dealership (not even taking it to a Toyota dealer, it seems...?), and oil changes. Doesn't seem quite right...

I've been wondering what I should check out on this car to see if there are some hidden issues that might turn into bigger ones. Being as old as it is, are there some things we should check out on the battery? Transmission? Engine? Engine seems to be running fine, but it almost seems to run *too* fine...

The problem I'm finding while driving, and the reason I figure I should post about it, is that it lacks acceleration... when I gently press on the gas, it seems to have very little power until the ICE kicks in, but then the ICE just kinda... boosts it a little. When trying to get up to freeway speed it almost feels like I'm murdering the ICE while pressing on the gas pedal... the engine whines like crazy and sounds like it's going about a billion RPM (a rough estimate without a tach, averaging the sound of my 2-cyl Ninja 250 and my 6-cyl Fiero engines, I'd say... 6k?). It almost seems to be free-wheeling with just a little of that power getting to the wheels.

The battery gauge is never full, either. Today, while I was letting it sit and run/charge for a while, it didn't make any progress towards topping off, but instead it dropped to half-full when I started driving. It never charged past half-full after that, but I didn't give it a long drive (2.5 miles)... it did spend a lot of time after it hit "half", trying to recharge the battery with the ICE.

These aren't typical behaviors are they?

 

HAH! Love that, "if you can acheive the speed that you wish to travel at on the freeway" - golden! Yeah, it gets up to a fast-lane speed and has no trouble staying there. I was just afraid of damaging the ICE by making it rev that high, so I don't usually push the pedal that much...

Good to know about the battery... I'll just let that be, then. Air filter is fine (checked that today), but the MPG had me a little concerned... their 300-mile average is something like 36 MPG (short 4-8 mile city trips). Is that about normal? :/

 

Awesome! Well, I guess that's that, then. Everything else seems to be just spiffy in the thing, although the brakes could probably use a little work - brake pedal is just way too damn sensitive. Goes from kinda-stopping to CLUNKstopped in like a fraction a millimeter... but maybe it's just because I've been driving an '87 Fiero for my whole driving life (brake has a niiice, smooth pressure transition from "slow down" to "omg slamonthebrakes"). Not a big deal but if it's something that sounds out of place I'll run it by 'em... not trying to be a "let's find something wrong with this car" thing, but I've just been concerned with their rather-slim maintenance folder - except for a whole steering rack replacement about a year ago