Feasibility of using 18V batteries to power AC tools
It's possible but not as easy as stringing them into an inverter.
DeWalt makes a device for this purpose in their 20v line.

https://www.dewalt.com/products/gear-and-equipment/generators-and-portable-power/1800-watt-portable-power-station-and-simultaneous-battery-charger/dcb1800b