I have an Omega quartz seamaster from 1979 and the battery is failing, where I live they can't source it and they won't tell me what battery numbersshould be. Does anyone know what battery number is it so I can buy it online and get someone to change it? I added photos of the watch. Thanks in advance.
It could be a 1342 movement but it's hard to say for sure without seeing it. Ideally you could take it somewhere where they can open the watch for you and you could take a picture. It's it's a 1342 the battery you need is a Type 392 or SR41W
Look very closely at the back of the watch -- if you are not as short-sighted as I am use a magnifying glass. You might find a number (possibly 1342 as @webvan says, I think quite likely for 1979), Yes, modern batteries are available but they need a sleeve to hold the smaller size into the case and they do not last as long as the 1970/80s mercury batteries.
Can you have a local watchmaker remove the caseback? That will reveal the battery and you can check the battery number. While it’s open you can also check the movement number and search for the correct battery number here - http://www.ranfft.de/cgi-bin/bidfun-db.cgi?10&ranfft&&2uswk If you can’t have the back removed, search for your model here x https://www.omegawatches.com/vintage-watches?product_collection=3179&v_watches_movement=2779, then google the model number and battery required. Good luck