With charged batteries in it and powered on 24/7 mine keeps pretty good time, but I do have to sync it when the batteries get weak and I failed to pull the power cord and reinstall at least once per week or so.
I‘ve noticed when changing out batteries if I take out the depleted batteries and let the unit sit for say 30 minutes then replace
the batteries with some freshly charged batteries I have to reset the time and date.
If I take out the depleted batteries and immediately replace them with new freshly charged batteries, the time and date stay current.
73, Rex
Thanks for the reminder, I forgot I can do it through the menu too. I also think I might have misunderstood the question because I gain about a minute every two weeks or so and the question referred to date and time. My date's always right but the time drifts.