He's dependent on other people for everything in life except the TV. It's the one thing he has left he hasn't lost control of, and guards it jealously. Sounds like Alzheimer's symptoms. It also sounds like you hate confrontation and avoid it at all costs. The proper Englishman stereotype, not saying that's a bad thing, just an observation.
Now I've been wearing hearing aids for 33 years x replace every 3 years x 2 ears = a shitload of hearing aids. I've never owned one that varied the volume with battery strength. Volume remained where it was set until the voltage dropped below a certain level, then the sound would shut off. Some had a warning where it would beep a couple times, every few minutes, for the last hour or so, but never changed volume.