Sandroidfan is on the money.
Don't touch task killers or battery managers. You don't need them.
Control the biggest battery hogs and everything will be fine.
1. Screen. Don't use auto brightness. Put a power widget on one of your screens for quick access to the settings. Set the brightness as low as you are comfortable. I keep mine at 10% and while I am indoors most days its plenty good for me. If I go somewhere bright I use the widget to bump it up to 30% while I need it.
2. Wifi. If you can use it, do so, as much as possible. 3G and 4G eat battery....especially 4G. If you have a weak signal and no Wifi at work there isn't much you can do about that. If you don't have 4G or you have poor 4G I would suggest setting your phone to CDMA only mode.
3. Syncing. Some apps background sync data a lot....and usually its not necessary. Google+ and photos are two apps that seem to keep the OS running way more than needed. Many of us have disabled these, and any other syncs that we don't need. I only sync gmail, email, calendar, contacts and browser. Most of the other apps/services you don't need to keep constantly updated. Things like twitter and facebook can update when you open the apps, and as long as you don't need instant notification that your buddy John had a great lunch today, you'll be better off.
Also keep in mind that talk time eats battery too. A lot of people forget that nowadays with all the focus on 'online communication'.
With these 'tweaks' I can get 20+ hours on a charge with 2-3 hours of screen-on time. I usually plug back in after about 16-18 hrs with 20-30% remaining. I've been as high as 29.5 hours with 3:45 of screen-on time. That said, 80+% of my time I am connected to Wifi so that's a big help.