I always understood that the Spotmatic SP-F and SP-II and later, had "bridge circuits" (which meant they weren't bothered by the small voltage difference between Mercury (1.35v) and Silver Oxide (1.5v) batteries.
So I have always used a Silver Oxide battery and had absolutely no exposure disasters.
Then I had one of my SP-Fs CLAD, and my serviceman suggested it be "adapted" to Silver Oxide batteries ( I had already been using them without any problem).
Well, who am I to argue with an expert, so I said OK, and it was done (as well as the CLA).
since the service, I have been using the SP-F (with Silver Oxide batteries) and can't say there is any really noticeable difference.
However, as part of the CLA there was also quite a bit of work done on the shutter (tidiying up the speeds, the blind etc), so an error in one part could have been compensated by another error in another part.