The battery drain problem of the OM's series is a result of a failure of an electronic component. The cameras did not have this problem when new. My only experience is with an OM-2SP (think that is right, had the LED readout). Bought it as the LED readout was marked as non-working. Took it apart, fixed the problem- then discovered the battery drain issue, sold it for parts. Someone on another forum needed the top and bottom plates. That was over 10 years ago. At this point, I would have made the mod to the battery cap, used AG-10 button cells, thinner than the original. A surface mount dual-position, single throw switch should mount in place and serve serve as an on/off switch. Project for when another $15 Black Olympus OM-2S comes my way.