I just recently picked up a Canon Datematic and cant get it to work. I'm pretty sure its the battery issue. I've read that you could replace the original 1.35 mercury batteries with a few LR44's and some tin foil. If anyone has some information on this camera it would be highly appreciated!
I needed to search for this camera, never heard of it. It looks like nice small rangefinder, with nice feature for date imprint ( http://camera-wiki.org/wiki/Canon_Datematic , manual is here: http://www.cameramanuals.org/canon_pdf/canon_datematic.pdf ).
In similar batteries issues (for example Rollei XF35) I have used RL44 with some aluminum foil that is used in the kitchen. I have noticed that lower iso helps to compensate higher voltage (used iso 250 in 400 film).