A battery monitoring device for a battery having cells grouped in modules. The device includes a monitoring circuit for each module which monitors the voltage in each cell and the overall module voltage. The monitoring circuits can also detect module temperatures. The monitoring circuits are networked to a control computer. The device can be used with a power supply and relays for each module to interrupt charging when a fault condition is detected by the monitoring circuits. Other features of the device allow equalization of cells having excessive voltages.