1. First, you call the inverter technician and ask him to check the inverter, the inverter should charge the battery. If there are any complaints in the inverter internal elements, it will not charge the battery. It may show a charging indication. But it will charge the battery. So if it is not charging, it will not feed when power is cut. 2. If the inverter condition is good, then check the battery. If the battery is kept idle for four months, the battery water gravity may be reduced. So you ask the technician to charge the battery for one day. The gravity of battery water may increase. If the gravity of battery water came to a good level, then you can use the same battery. If it is not then change the battery.