A: A really freaking long time!
I've started to put together a bench 25 years after I lost all my TVs, test equipment, and stock of replacement parts. My first purchase was this sweet RCA VTVM, from a guy in Italy on eBay. It's a 220V European model (who knew?)
Opening up the case I was quite surprised to see the original RCA-branded dry cell still soldered in place, and showing almost full voltage!
I've since cleaned the meter up, replaced a rotted power cord, and tested the probe to find it showing infinite resistance. I managed to get it apart, but just the cable shows a resistance between 0 and 5 ohms that varies when you move it around - it's also not very flexible anymore.
The sensible thing seems to be to replace the entire probe and cable assembly. I've seen new "replacements" on eBay but they are just cheap VOM-type probes. Anyone have a suggestion for something that's a little more like the original? And maybe incorporates the AC/DC switch? I'd be willing to get rid of the UHF connector and replace it with a BNC too, I suppose.