Need help. What battery for my Seamaster 2262.50?

Or more specifically, my wife's! I've spent some time searching for the correct battery reference no., for my Wife's Seamaster 2262.50, though, regardless of brand, I have been able to find nothing.

Maxell or Seizaken have been recommended, but without taking the back off, I have not been able to find a reference point from which to order.

Any help would be appreciated. Other than that, I'll just take the back off, ( I attempt to keep this to a minimum) and move on from there.

Thanks

Mark

Thanks Al. Appreciated..