I bought an OM 1 recently (serial number is 986689 so presumably an early one) which has a fresh (I think) Varta V 625 PX battery in it. I haven't been able to find much info about this battery but it appears that this is a 1.5v battery which, according to what I've read here and elsewhere, will throw the meter out by about 3 stops. I use negative film so this won't be a problem.
I had the camera CLA'd and the meter has been calibrated, presumably to work with the 1.5v battery. The fellow said that using 1.5v batteries isn't a problem because the camera has a voltage regulator (which I don't think is true according to what I've read).
Should I just keep using V625U (1.5v) batteries and let the latitude of the neg film cope with the meter inaccuracy, or would it be best to buy the MR9 adaptor that John Hermanson sells? Would the meter need re-calibrating if I use the MR9?