Hi, recommended UK supplier:-
http://www.smallbattery.company.org.uk
My Casio watch has two different batteries, both of which had expired.
As 5 years ago Casio charged £15 to replace, this time I decided to replace myself, although not straightforward as a retaining cage is used, which appeared difficult to release.
A local watch repairer advised he had neither in stock, but could order for around £5 each.
Thus I ordered midday Thursday from the above website and they arrived early Friday.
Total cost - £3.34.
me on the way to the bank!.
Regards - Mike