Why does recovery obliterate battery life

[justlaxin13]

Hey, just always wondered why booting into recovery (any recovery, CM, EE whatever) completely annihilates battery life. This has been true for both android phones i've owned. Just now I booted into CM recovery just to check something, i did no flashing, deleting or anything. I was in it for maybe 10 seconds before i restarted my phone and i went from 46% battery to 12%. This is fairly typical whenever i use recovery...why does this happen?

 

[anon(94115)]

Never saw anything like that using CWM or amon ra recoveries.