Abstract: A system is disclosed for monitoring the state of charge of batteries in a fleet of electrically powered vehicles. Each battery has associated with it an integrator module which registers both the depletion and charging of the battery. While the battery is in use in the vehicle, a portion of the current flowing from the battery is sent to the integrator module which registers the current depletion. A readout circuit is also coupled to the integrating device for indicating the condition of the battery while it is in the vehicle. When the battery reaches a predetermined low state of charge, circuitry provided for detecting this condition provides a prewarning signal and on further discharge disables nonessential auxiliary functions in the vehicle, leaving only those systems working which are necessary in order for the driver to be able to return to a battery charging station. At the charging station, the integrator module and the battery are removed from the vehicle and connected at the charging station.

Abstract: A coulometer signaling device is disclosed which indicates when a particular machine has been used for a predetermined amount of time. The device comprises a mercury coulometer which includes an electrolyte whose color changes when the mercury deposited on the anode of the coulometer has been depleted. The end of the tube near the coulometer is somewhat enlarged and a lens is placed over this end in order to make the color change more visible.