Thanks Nigel for the explanation that could also be applied to laptop computers

Unlike a Desktop PC My Dell laptop Computer had no internal CMOS battery that could be replaced just a capacitor soldered to its motherboard this was the backup unfortunately when this component dies it can be an expensive job to get it repaired so I tell everyone to connect you laptop into the mains every so often to keep it charged so the best advice would be to boot up your Keyboard every so often and do not leave it standing around unused for months