A week or so I purchased an air tank, and tonight I went to go fill it up. (For being a container that holds air, it gets to be uncomfortably heavy after a while...) Then, I treated Segway to its first weekly-to-monthly tire refill. (Yeah, I was half a year late.) It's amazing how much better it rides on 15.0 PSI compared to 5.5 PSI. It doesn't even make awful noises anymore. I thought the batteries were dying prematurely or I had gained a lot of weight or something. Nope. Just needed to follow the instructions that came with the thing and keep its tires full. I'm such an idiot.
UPDATE: After riding it this morning, I am even more angry that I waited so long. It goes up hills at almost full speed once again now, instead of like 5 mph. The handling is back to the way it was when I first got the thing. (The ride is, unfortunately, a little more bumpy on the horrid sidewalks near my apartment.)