In short: yes, 3G is much heavier on battery, it is always active when wifi is on and there is no way to disable 3G only. If wifi is not turned off before sleep then the Kindle even contacts Amazon servers periodically via 3G during the sleep.
You can disable indexing temporarily by these commands:
Code:
;debugOn
~disableIndexing
see this thread for more information:
https://www.mobileread.com/forums/sho...d.php?t=116981