The Kobo may very well last longer because I turn on wireless less frequently and for less time, that's true
I didn't realize I could update the metadata in the Kindle for a book I didn't sideload. That may well help with preferring the Kindle since it isn't often Kobo has a book Amazon doesn't or at a better price. And I learned today Amazon has the Kindle First program and the Kindle Owners Lending Library.