I have just stumbled across this old post and found it very useful... After sitting is a drawer for years, my Minidisc MZ-N710 would not power up and made clicking sounds when on the cradle. I found that the gumstick battery had leaked and the battery cover was crusted shut. I managed to get it open, bought a new battery (£2.99 off eBay) but could not get it to charge, I read @tphil post above about the poor design of the lower contact, so bought some electronic cleaning solvent and using an cotton earbud, cleaned the lower contacts - and hey presto, my battery is now charging! I am very pleased, so thank you for the information. This is what the internet is about :-)
