My 8820 can go days between charges. The 8820 has excellent battery life. SO you either have something running in the background or your device is defective. I am betting you have something running. You, yourself said that when you unlocked BB Maps your battery started draining "insanely"! So what do you think!

Also L-Ion batteries do not like to be run to near empty before charging, this will only shorten the life of the battery.