For further information about watch batteries; their chemistry, numbering, watch battery prefixes and Note, that the lithium watch batteries, or button cells, are 3 volts, not 1.5 volts and cannot be substituted for a 1.5 volt silver oxide watch battery or alkaline Mercury watch batteries are no longer manufactured so your only alternative is to use a silver oxide watch battery of the same size. You should

Renata 377 SR626SW 1.55v Silver Oxide Watch battery Renata 377 SR626SW 1.55v Silver Oxide Watch battery

the CR927 3V lithium battery. This mistake in the handbook appears across several different models of Casio solar calculators. or height). This will give you an idea of which watch battery to choose if you do not have a watch battery cross reference number to match the battery against. this is a lithium battery. The handbook is wrong! The replacement for the National GR927 is the 399 silver oxide battery and notIf you are replacing a National GR927 battery in a Casio calculator please note that your calculator handbook is likely to say that The Watch Battery Cross Reference Table below gives all Watch Battery sizes and their equivalent replacement watch battery reference