Why is the Charge screen not appearing

Just recently when I put my iPod nano 2Gen (8GB, black) on to charge, the charge screen with the large green battery on it sometimes does not appear when I switch it off. Instead the screen just goes blank

It seems to happen particularly if I only used a little bit of battery and want to top it up ready for a long day out ahead at the weekend. I think it might be doing some charing because when I switch it on, the small battery icon appears in the top right hand corner of the menu with the “charging” lightning bolt across it, but I don’t know if it is still charging, once the screen goes blank.

Occasionally I do sometimes manage to trigger the charge screen, particularly if the battery is very worn down, but I can never quite remember how I managed it. The charge screen with the big battery icon used to just come on automatically whenever I plugged the iPod nano into the mains.

I know it’s not a problem with the charging cable nor the mains plug because, like I said. it’s showing the little charging battery icon in the top right corner of the menu.

The iPod was bought second-hand about 4 or 5 years ago.

UPDATE: I have just now managed to get the charge screen to come up and it is showing the big battery sign with the plug, meaning fully charged. I did this by swtiching it off while it was on the system info screen. However I have switched it off several times before recently without it going into the charge screen and I don’t quite understand what it is that I got right this time that I didn’t get right earlier today.