Analog film photography and cameras

small voltage/resistance/current meters are useful things to have around the house.

otherwise, from http://www.kenrockwell.com/pentax/35mm/cameras/me.htm:

Battery Check

The viewfinder LEDs should stay on for a while when you tap the shutter and the film advance lever is pulled out.

If they turn off immediately when you take your finger off the shutter with the lever out, the batteries are low.