Firmware 4.2.1 drains power very fast iPhone 3G

After ive upgraded my Firmware to 4.2.1 it seems my 3GS is drained from power very fast !
Yesterday at 7pm i drove to a restaurrent using Navigon, the iPhone where at 100% battery + charged in the car.
when i got home and went to bed, the phone was down to 30%
when i was supposed to wake up, the phone had turned off !!
I repeatedly HAVE TO CLOSE ALL BACKGROUND PROGRAMS ALL THE TIME to be sure the power isnt drained while off ....
If i could disable background tasks i would do so !
im so tired of power-drains like this
Lenovo T400 / P8600 / 2GB Insanely fast laptop