High CPU usage when doing light browsing effecting battery life

Uninstall Avast according to the Avast maker's instructions -- it's not needed. You could try restarting in safe mode and look at the Activity Monitor to see how much it changes. The iStat entries won't be there then. In safe mode check activity monitor to see how much CPU Time opendirectoryd is using -- It's generally at 0% on my machine. Booting into safe mode can sometimes fix problems. Close any open apps when you aren't using them as they can be a drain.

Turn off InternetSharing in System Settings unless you are sharing you internet connection with other devices. That will save a bit.

Do you have any anti-virus, "Mac Cleaner" or "Mac Optimizer" software installed? These can be huge power hogs when operating in the background (as well as create more problems than they prevent).