Casio watches' warranty does not include battery life.
addition, the life of the watch battery (e.g. the Casio LW-200D series
which has 10 year battery life from the date of manufactured) will
depend on the wearer's use on the watch. If the light and all buttons on
the watch are pressed once every day, the battery will worn out faster
compared to someone who pressed the buttons every few days. This is very
subjected to a wearer's lifestyle. Just an indication, according to one
of our colleague who also has a Casio 10 year battery watch, his
watch's battery worn off about 9 years plus.