Actually it's the opposite. The camera runs off of 1.5v silver oxide batteries, and the manual warns against using similarly shaped 1.3v mercury batteries. The other thing is that the meter that I tested isn't used for the actual exposure. I'm wondering if the off the film meter has the same inaccuracies.
I am a little confused about what you are saying about metering.
What is it you are using as your "target" when you are checking the metering? Is it a grey card or other even surface, or a scene with a variety of light and dark areas?
If it is a scene, than the difference may be due to the OM2 meter reading pattern being centre weighted differently than the Elan cameras.
The off the film metering is, in my experience, very accurate, but it is, of course, only applicable when you use automatic exposure.
Two things to check with respect to the OM2:
1) this is probably too obvious, but make sure you don't have the exposure override turned on; and
2) there are two different sets of focusing screens for the OM cameras. IIRC, some of the newer series (which are brighter) are not really suitable to the older cameras, unless they are adjusted for, because they cause the in viewfinder readouts to be in error. This does not, of course, have any effect on the off the film metering.
Hope this helps.
Matt