That's the version I have - also a 'Spotmatic From Heaven'; I purchased three lenses from a member here and he threw in three bodies as lens caps! The SP-II is a peach. I just had mine out about a week ago.
I use an Energizer 394/380 with mine. My camera came equipped with a little white-ish plastic spacer specifically for the purpose of adapting it to that battery compartment. If I'm not mistaken, you can purchase a
387S, which is the same battery but with that little spacer included, and then just buy 394/380's in the future, reusing the spacer. As others have pointed out, the meter circuit in Spotties is not very fussy about voltage: close is close enough.