Hello,
I think this is an early Leicameter with a selenium cell. Nearly all Leicameters with selenium cells I saw were dead and no spare parts are available. The later CdS types like the MR-4 require a mercury cell which is no longer available, maybe a zinc/air Wein Cell or a MR-9 adapter can be used. The plastic lid of the battery compartment is easy to break. I find that the MR-4 is not very useful as he has two measuring ranges and the border between them is just in the range of usual light conditions. When you carry a M-Leica with mounted Leicameter, the ASA setting is easily misadjusted as the ring rotates when in contact with your cloth. The measuring angle of the CdS meter is in the range of a 90 mm lens, the older selenium types have an angle of about a 50 mm lens.