Those apps aren't entirely accurate. I wouldn't rely on them entirely. The one I prefer is coconutBattery (http://www.coconut-flavour.com/coconutbattery/) but it requires a Mac (then connecting your phone to the Mac).
Even that can have a little bit of a variance especially if the phone isn't 100% charged. I only record % from design capacity when the phone is 100% charged and I see a 1-2% variance.
For example, when my phone was 60% --- the design capacity once showed a 6% difference. That 6% difference went away when the phone was charged to 100%.