Although not immediately obvious, there is a distinct difference in battery usage depending on whether the tablet is turned off with the power switch or whether it is allowed to turn off with the Timeout feature.
When the tablet is left idle for the period of time set in the Sleep feature (anywhere from 15 seconds to 30 minutes), the tablet power is not turned off, although it may appear to be. In this state, the power to the screen is turned off, but applications and services are still running in memory and will continue to drain power from the battery. This can result in you returning to the tablet later, only to find the battery unexpectedly drained.
To avoid this, when the tablet will be idle for more than an hour, it is recommended that the tablet either be connected to AC Power or be completely turned off. This will ensure the tablet is either charging or drawing as little power as possible.
NOTE: To completely turn off the tablet, press and hold the Power button until the Power off prompt is displayed, and then tap OK.