Inverter lasts for 1 hour or less

The service was excellent and hassle free when i bought my inverter in June 2022. The reason for my one star rating is because the inverter does not last even 1 hour even though it was advertised that it lasts 4 hours. We are now in December and the phone lines are not working. I have sent an email which will hopefully get responded to soon as GeeWiz will be closed from the 16th to the 09th of January. I am disappointed in the quality of the inverter to be honest.