A cell phone with 0 charge shows the time. Latest experimental as of time of posting.
It has the item flag that shows time no matter what happens to the item possessing the flag.
It shouldn’t be hard to fix this issue.
PR’ed a fix (https://github.com/CleverRaven/Cataclysm-DDA/pull/28485).
Couldn’t you just set up the item to transform when not charged? The charged version keeps the “WATCH” flag and the uncharged one doesn’t.
It’s not as simple as your initial solution, but it would allow for more control, letting you adjust individual items without making a blanket change.
I’ve never used transformations, though, so maybe I’m not really understanding it.