I use hearing aid batteries. To set the asa I just meter something with my Sekonic. Say it says f16 at 1/250 for 400 asa. I then set the f stop and shutter speed on the camera and then adjust the asa dial until the meter needles line up. Works like a charm. Typically the asa ends up being set to 1/2 of the rated asa. ie 400 asa film is dialed in at 200 asa on the camera. ymmv.