"Antique" Casio kids digital watch (Whitegrove RG42)

This is quite an old kids watch that belonged to one of my boys now in their 30's but it is still working! I have no memory of changing the battery in it but it is still running. Still looks quite smart. I don't have a user guide for it so you will need to download one from the internet to work out what all the buttons do. This is definitely for a child as the strap will not fit round an adult wrist.