My H340's battery completely died a week or two ago, after more and more rapidly running out of juice.
A friend had success with putting batteries for various electronic devices in a freezer to reset them and I saw some passing references to this trick on this forum. So I took the battery out, put it in a ziplock freezer bag, froze it for 24 hours, let it thaw for 12+ hours and put it back in my iriver.
Works like a dream now.
Probably not news to a lot of people, but I did a bunch of searches prior to trying it out and couldn't see anyone on misticriver saying that it had worked for them.