A client of ours had got a Kindle recently and seemed happy with it but the batteries kept going flat. I checked and it seemed to be charging fine so I dug a bit deeper and this what I found.
The PC is a brand new laptop running Windows 7 Home Premium – I know as I re-installed that as English a few weeks ago. The power management was left as the default of Balanced.
The quirk with this is that they leave the Kindle plugged in when they go out but the Balanced power setting on Windows 7 by default shuts the PC down in 30 minutes (when on mains) when idle.
The Kindle needs 4 – 6 hours to charge thus it will never really charge unless you stop the Laptop from going into power save mode. I changed the Balanced on-mains power shutdown period to 4 hours to at least give the Kindle a chance to get a charge.
I imagine that other people have had this without really thinking about what is happening.