Larry's wife wants to back up her Kindle eBooks onto an SD card to read on another device. Leo says that Kindle uses MOBI as its file version, and it can only be read by Kindle. She'll need to convert the files to ePub, which is a standard format. Leo likes Calibre for that. If she uses the Kindle app, then it's no problem, and she can just install the MOBI files to that other device. She'll need the folder structure first, so she should download a new book on the new device with the Kindle app. Then she can move them over.