It seems 390/389 alkaline button cells can power the mini-lathe’s DROs for about a year:

Given that the replacement cells all come from the same batch, they’re aging on the shelf as well as in the DROs.
Once again, I replaced both of them.
The Smell of Molten Projects in the Morning
Ed Nisley's Blog: shop notes, electronics, firmware, machinery, 3D printing, and curiosities
It seems 390/389 alkaline button cells can power the mini-lathe’s DROs for about a year:
Given that the replacement cells all come from the same batch, they’re aging on the shelf as well as in the DROs.
Once again, I replaced both of them.