You idiots, deleting "important files" doesn't lower battery life, it just stops the computer from booting.
The issue is more likely that you reset or disabled the power saving features of the laptop (such as Intelli-step).
First step is to go to the Control Panel and to Power/Battery Settings. Play around with the settings and see what works for you.
Other things to consider:
Is there a disk in the drive? the drive uses a lot of power when it is in operation.
Have you been nice to your battery? be sure to fully discharge and recharge the battery each time.
I have probably forgotten some other stuff too.