A Call to Coastguard Eastern Region from 5m aluminuim runabout with three people on board that had its motor swamped while crossing Whakatane bar. While trying to start the motor the battery was flattened.  Whakatane Coastguard was notified and the local Duty Officer responded. An all stations request was made for assistance and a good samaritan offered to assist. After assessing the problem the good samaritan returned to port, removed the battery from their truck and took the good battery out to the disabled boat.  The motor was started and the boat returned safely to port.  Whakatane Coastguard sincerely thanks the good samaritan for its assistance.