I 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.