Some great stuff - many thanks. I will consider buying a battery and have looked on youtube - the process looks very straightforward although I will be a little disappointed if I've only had 18 months or so out of it.
I take the point about indexing - in fact the kindle had gone really slow as I'd been messing about with collections etc. I've now removed all books (around 700(!)) and collections and reinstalled them.
Watch & wait for the moment I think.