No, there is no internal battery to charge. The inverter uses a 12V battery to generate AC and USB power.
There may not be enough input voltage to power what you have plugged in. To reset it, turn the unit off, disconnect the unit, unplug everything. Carefully re-connect the unit, turn it on, and then plug in your items.
The cooling fan is designed to come on only when the inverter reaches a pre-set temperature to save power draw from your battery.
1) Check the voltage at the inverter input with the load on the output and see if it is dropping the battery below 11 volts. 2) The cables may be too long, and the voltage drop may be causing the alarm to sound.
No, but you can hook a solar panel with a charge controller to a 12v battery then connect the inverter to the 12V battery.
No, this inverter is designed for 12V Lead Acid batteries.
You can not pull more power through the inverter than it is designed to provide.
Volts refers to the power source your inverter is connected to; watts refers to what you have plugged into the inverter.
The inverter is in overload protection mode, the device plugged into the inverter requires more power than the inverter is capable of.
The fan is controlled by internal inverter temperature so the fan can turn on even when the unit is not under load.
There may be a faint buzzing sound, which is normal.