Battery Widget APP
The font size can be changed in the widget settings, e.g. when adding it to the screen for the first time. The default widget size is 1x1, but you can resize the widget by long-pressing on it then dragging the resize handles.
Due to Android power-saving restrictions, it will only update once every 30 minutes by default. You can make it update more often in the configuration settings, though this takes extra power and may drain your battery. You can also click on the widget to update it to show the current battery level. Unfortunately it has to update based on a timer, it can't monitor the battery level constantly like the built-in Android battery widget since the built-in Android battery widget uses special system permissions which 3rd-party apps can't use.
Please note this app doesn't appear in the Applications list since it's just a widget. After installing it, you can add it to your home screen by long-pressing in an empty area on your home screen, which should bring up a menu which includes an option called 'Widgets'. Select 'Widgets', then look for 'Battery Widget', and long-drag the widget into the empty space on your home screen to add it there.