Hi Guys, after a little more investigation it turns out that the seller sent the wrong charger - a 4.5v Sony (probably from a PCDP) instead of the required 6v charger - which is why the battery wasn't charging. It is going to be a lot simpler (and cheaper) to get a replacement charger than try to source a proprietary battery for a player long discontinued and then get it fitted. Thanks for all your help. I like this forum - think I'll stick around for a bit.