An electrical charging system for charging an autonomous robot powered by a re-chargeable battery and having a first charging member. The charging station includes a second charging member configured to receive the first charging member on the autonomous robot when the autonomous robot is docked with the charging station for charging the re-chargeable battery. There is a power supply configured to charge the re-chargeable battery of the robot and a sensor configured to measure an amount of charge transferred from the power supply to the robot. There is a processor configured to determine from the amount of charge transferred from the power supply to the robot measured by the sensor, a state of charge (SOC) of the autonomous robot. There is also a communications device configured to transmit to the robot the SOC of the robot while docked at the charging station.