Portable CD Players

Mine usually lasted 4 hours or so. I've never noticed the music really deteriorating in quality, but some of them do have a little light that goes on when the batteries get low.

Usually the volume starts to go. You'll notice you have to turn the dial up if you haven't got it full bore in the first place (and neither you should, of course!)

There is a dramatic decrease in battery life if you use them in cold places (below freezing). You can sometimes bring them alive again if you take them indoors and let them warm up again but not for very long.

Perhaps as little as an hour with new batteries.

When portable CD players first became available, nobody made he higher powered batteries for electronics that they do now. Mine had a radio in it. If you just used the radio the batteries would last a little longer, but CDs ate the batteries in a few hours.