The most common cause of failure of an inverter is an improper installation. Apart from this, other things that can hinder the smooth charging of an inverter are: Dead Batteries:

When a battery is getting too weak and needs replacing, your system may send you an alert or show ‘Lo Bat’ on the keypad display. The Alarm Panel requires (1)

What is a 12V constant wire? The 12V accessory wire is connected from the stereo to the ignition switch accessory wires. So when you turn on the ignition, it activates