alt Hacker NewsI remember how badly these radios would drift off-time when running on the battery backup! He explains in the article about how the back-up oscillator is a simple R-C circuit because the power line reference is absent.
It would also kill the backup battery in a couple of hours. If you're in an area with prolonged, frequent backups it wasn't worth installing the battery. It was only good for occasional, short blackouts of a few seconds or less.
Probably didn't help that your 1980s and 1990s 9V battery was likely a zinc-carbon battery, about 1/2 - 1/5th the mA of alkaline.
I do remember that I could unplug and replug my alarm clock pretty quickly and it wouldn't lose its time if I needed to move sockets. Yay capacitors?