Sub Date not retaining power reserve

[CoopJr]

I saw my dad tonight, I asked how his watch was when I did not see it on his wrist. He said it's OK but "loses power".

After some questioning he says that if removed for a day, the power reserve runs out. I thought that the last servicing he had a few years ago was done by a RSC but was instead done by some local Yahoo

I searched TRF but could not find the exact reason as to what may be causing this....input appreciated and needed