true but each of the OMs are different.
a simple CdS cell draws no current in a changing bag but a off on switch is desirable as they will work (draw current) in overcast moonlight even if the meter or coupling does not register it.
Only the OM1n and OM1 have a CdS cell.
The other OMs have photocells which react more quickly for offthe film or shutter curtain metering and spot metering depending on model.
I normally omit the battery from my OM1s.
Unnecessary complication, bit like a phone in pocket really.
Though with an F5 you can show people you have not taken their photo.
hee hee hee