I've got an 860 and regularly use my old sl 5500 batteries in it whenever my larger batter runs dry. Be forewarned though, that the life of the charge is dismal compared to the proper larger battery. I can leave my 860 playing music for about 8-10 hours as a guess at least, but with my 5500 battery that is halved. With the screen on you will want to put the brightness to lowest to get anything reasonable.