There is a trick to revive a flat battery, won't always work, but worth a try.

Using a charger and forcing the process for a couple of minutes, the Clam will probably will be able to charge again.

http://forum.macbidouille.com/index.php?showtopic=326723&pid=3248037&mode=threaded&start=&do=findComment&comment=3248037

the Text is in french, but you will probably catch the idea.