I saw a strange product at a 100yen shop. The plastic cover changes an AA battery to a C battery (there was also a version for AA to D). I probably wouldn't buy them but it is an interesting idea. These days I've been super busy and I don't have time to update LDK (although I have time to go to 100yen shop!). I hope I can come back on Wednesday and update everyday. Thanks for all the comments, sorry for not replying!