I use a cheapo from Lidl/Aldi; the one that looks like 2×6" steel rules on a pivot with a little DRO.
Like the cheap digital calipers, they seem to stop reading after a while as the centre battery contact corrodes slightly, and not always visibly.
This is particularly the case where I've used cheap replacement batteries; the ones where you get loads on a bubble/card display pack. They seem more susceptible to it, but I normally keep a cardfull in stock for emergencies.
A quick wipe with a glass-fibre pencil and a feint smearing of Vaseline/silicon grease holds the problem at bay for quite a long time.
For the fibge pencil, I use a length of strengthening member from a fibre optic cable; I saved a few lengths from out of the scrap bin when I worked for BT. It makes a good mouse for feeding wires under floorboards too.
If you have Telecom contacts who work with fibre cables, make discrete enquiries; the orange sheathed stuff works better than the later white variety.