Chuffed to bits with my Chronos clock ... until it stopped working

. Bought some new batteries, fitted the replacement (fiddly - but easy) - same result.
The seller couldn't have been more obliging - sent a replacement clock by return of post ... which has now also stopped

Has anyone else had this problem? I'm so glad I didn't drill the dash to fit the mount (or even worse - cut a hole!). At least if I can't get one that keeps working long term, I've not ruined the dash.