I have some 20 year old but new condition digital B&S mikes and a Starret depth gauge that had the batteries die a very long time ago. The Starret digits started getting wonky and then quit B&S just refused to turn on. Both with new batteries.
Junk? Of can the factory reflash them? Guessing part of the ROM lost its memory.
LCD's missing digits over time is almost always the elastomeric 'zebra strip' which can be cleaned & repaired or replaced by a competent repair person. Corrosion, either contacts or internal components are the most likely cause of any other issues. These devices, especially older designs, are nowhere near sophisticated enough to require programmable ROM or flash memory, that's not the issue.
It's very unlikely that it would be cost effective to pay someone to fix them, but if you are willing and able to research and teach yourself some simple repair skills it is possible you may be able to repair them yourself. Depending on condition and utility they may still have value to someone who can repair them (although I would strongly encourage you to not touch them in that case and make it clear that they are untampered with when selling them.)