Battery consumption with the OM2SP and the OM4 was not one of their finer points. The later OM4 models and the OM4Ti were OK after the circuit boards were modified. There was a way to tell which model of the OM4 was OK but I cannot recall at this minute.
I am not an expert, but as far as I know there never were later OM-4 models that did not suffer from the battery drain problem. There are OM-4 camera's with updated electronics, but Olympus only replaced the boards of camera's that came in for repair. The way to find out if a OM-4 model has an updated circuit board is to switch the camera to battery check mode. If the battery is full, the camera beeps. If the beeping stops after 30 seconds or so, the battery has the updated board. If the beeping does not stop, the camera has not been updated. The OM-4T or OM-4Ti never suffered from the battery drain problem.