Buy the GSam Battery Monitor at the Amazon App Store. Then leave it on their icon screen when charging. It shows graphically the situation as it charges and the time left for a full charge. Since there is no battery LED on the HD, the GSam Battery Monitor is really a necessity just for that purpose.
I close the cover which puts the KFHD in sleep mode when charging and then open it from time to time to look at the GSam icon screen to see how much time is left.
For a full charge on my KFHD7-32 it takes six hours. That charge then lasts for 6 hours of actual use. In sleep mode it uses no power as determined by the GSam Battery Monitor.
You can purchase it here:
I leave WiFi on all the time. The GSam Monitor shows:
The Screen uses 45% of Energy and WiFi uses 16% of Energy - not really material. The System and its accessories use 14% of Energy.
I notice no materai difference between using Shut Down Mode versus Sleep Mode other than a very slight drain due to the WiFi being on but rarely really used in Sleep Mode. It would only be used if firmware or apps are updated while in Sleep Mode.
You will also need their advanced icon pack here: