I think SCC is correct - it sounds like the button batteries were dying. It's kind of amazing that they could still power the viewfinder LEDs. Taking the batteries out will not affect any exposures already on the film.
It *is* possible to use an ME/MV/MG with no batteries in 100X (Flash sync) mode using the "sunny 16 rule", but that requires some old-school light estimation skills and a lot of practice. B mode (B for "Bulb", as in old-old-school flash bulbs.) doesn't use batteries because it just holds the shutter open as long as the shutter button is pressed. I've used B for long multi-second exposures by counting the seconds out loud, but unless you are really really good at estimating fractions of a second
, it's useless for most exposures.
Side note: Asahi Optical Company (AOCo) was the name of Pentax' parent company until 2002. The model name is just Pentax MV.