The Pentax Spotmeter V takes SR44 silver oxide cells, just like many cameras like the Nikon F3 and the Olympus OM4T. They're sold all over, even Walmart sells them. Beware, though, that older Pentax meters, like the 1/21, use Mercury batteries that are no longer made.
I have a Minolta Spotmeter F and I love it. It is very accurate, small, and reliable, and as you noted it takes AA batteries.