My CD player lasted for two hours on alkaline batteries. Or, with cheap zinc batteries from Asda, the duration of one and a half Blink 182 albums during Maths on a Monday afternoon.
Ah by the time it came for me to not want to listen to teachers MP3 players were already around.
I was rocking a generic 512MB for years 10 through 11 at school. Also having long hair means no one can see you've got headphones in.