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//// A few years ago I bought a gimmick or removing watch-backs. Nowadays I remove the back, look up the battery number, buy some more and change it myself. Look on Amazon for "Watch back Remover". They're only a few pounds, cheap enough that you'll save the cost with just one battery. ////
Yea I've got all the gear plus loads of batteries, a full set of various sizes of pins etc, so if one of my pin snaps I always replace it myself. I opened up the back myself with one of my tools and looked for a battery, only to find I didn't have any. I knew Timpsons were expensive, but I thought I'd pop in whilst I was in town .... still amazed at the price, even though they try and justify it with the pressure test etc.
After I fit the new battery, I just tightened my watch up fairly tightly, not too tight. I probably won't use it whilst swimming anyway, so I'm not really bothered if it's waterproof or not.