What are the charging instructions for the Stanley FatMax professional power station?

The unit arrives partially charged and must be fully charged before first use. Lift the protective cover of the built-in 120-volt AC charger on the lower left front, connect an extension cord, and plug into a standard 120-volt AC outlet. Charge for approximately 40 hours or until the Battery Status Icon shows 4 solid bars. When complete, unplug the extension cord from the outlet and disconnect it from the unit. (Page 9)