To my knowledge battery apps are using somewhat of the same method or function call to the android operating system to get the level of battery.
The stock battery icon in the bar is misleading. I remember after first installing a few battery apps noting that if the battery is really at %49 percent the stock battery meter at the top shows closer to 1/3 of the little battery full. So its really the stock battery meter in my opinion that is responsible for your confusion.
Some battery monitoring widgets or meters can be a waste to the battery itself. You'll find a lot of members of this forum and all over are using the one called:
Battery Indicator
Instead of a widget on the home screens it puts a icon on the left side of your status bar with percentage. When you pull the notification bar down it tells you things like: time last on charger, voltage, health and battery temp.
Cheers!