After installation, why there is no icon shown in the application list.

Battery Widget for Android is not an application, but an widget, hence there will not be any icon show up in the application list. It will only appear in the Widget list. Please consult your respective user manual for the phone/tablet on how to add widget to the home screen.

Is widget available on lock screen?

Widget can be added to lock screen for Android version 4.2 and above. However, the lock screen widgets are no longer available under Android version 5.0.x.

Is the widget resizable?

Depending on the Android version, Widget is resizable with Android version 3.1 and above.

How to get more themes?

Tap on the Widget to bring up the menu, select ‘Themes’, click the ‘Browse for More Themes’ button, list of available themes will be displayed in the Google Play Store.