Normally when I travel, I put my laptop into sleep mode. However, very often when I switch-on my laptop a few hours later after sitting in the plane, I realise about half of my laptop has already been drained out. I wonder, what could be the cause of this and how can this be best avoided? Also, i wonder, is Hibernation a better option than "sleep" in such situations to make sure, I do not lose any battery while the laptop is in my bag?
Sleep essentially leaves the computer running to keep the what is stored in memory active. Every refresh cycle it drains the battery a little more.
Hibernation takes what is in memory and writes it to disc, then shuts down. On reboot it loads that information back into memory. Essentially preserving the computer in whatever state it was before you asked it to hibernate.(This is the default 'shutdown' behavior of Windows 8 by the way)