Is it battery drainage right after rebooting your phone or is it faster battery drain over a period of time (e.g. several hours)? If it's right after rebooting, I reckon that's normal as I notice it on my N900.
restarting n900 need 10% battery power on standar condition.depending on how much application inside hildon menu. hildon home and auto run. it could reach more than 10% even 15 % percent.