A system for charging a battery string that comprises first and second half-strings electrically connected at a mid-point, each half-string comprising a respective plurality of battery modules connected in series, each battery module comprising a respective plurality of battery cells, the system comprising: a first plurality of sensors (3a-3c) connected to sense a full-string voltage measured across the battery string, a first half-string voltage measured across the first half-string, and a second half-string voltage measured across the second half-string; a failsafe overcharge system comprising a first disconnect device (17, 72) and a processor connected to receive sensor data from the first plurality of sensors during charging and send commands to the first disconnect device, a power distribution bus which is electrically connected to the battery string via the first disconnect device when the first disconnect device is closed; a battery charger connected and configured to supply battery power to the power distribution bus for charging of the battery string, wherein the processor of the failsafe overcharge system is configured to send a command to open the first disconnect device when the sensor data from the first plurality of sensors indicates an undesirable electrical state during charging that would be mitigated by cessation of charging, a second plurality of sensors connected to sense battery cell voltage and temperature of each of the plurality of battery cells; and a battery management system comprising a second disconnect device (17, 72) and a processor connected to receive sensor data from the second plurality of sensors during charging and send commands to the second disconnect device, wherein the power distribution bus is electrically connected to the battery string via the first and second disconnect devices when both the first and second disconnect devices are closed; and wherein the processor of the battery management system is configured to send a command to open the second disconnect device when the sensor data from the second plurality of sensors indicates an undesirable electrical state during charging that would be mitigated by cessation of charging. a first plurality of sensors (3a-3c) connected to sense a full-string voltage measured across the battery string, a first half-string voltage measured across the first half-string, and a second half-string voltage measured across the second half-string; a failsafe overcharge system comprising a first disconnect device (17, 72) and a processor connected to receive sensor data from the first plurality of sensors during charging and send commands to the first disconnect device, a power distribution bus which is electrically connected to the battery string via the first disconnect device when the first disconnect device is closed; a battery charger connected and configured to supply battery power to the power distribution bus for charging of the battery string, wherein the processor of the failsafe overcharge system is configured to send a command to open the first disconnect device when the sensor data from the first plurality of sensors indicates an undesirable electrical state during charging that would be mitigated by cessation of charging, a second plurality of sensors connected to sense battery cell voltage and temperature of each of the plurality of battery cells; and a battery management system comprising a second disconnect device (17, 72) and a processor connected to receive sensor data from the second plurality of sensors during charging and send commands to the second disconnect device, wherein the power distribution bus is electrically connected to the battery string via the first and second disconnect devices when both the first and second disconnect devices are closed; and wherein the processor of the battery management system is configured to send a command to open the second disconnect device when the sensor data from the second plurality of sensors indicates an undesirable electrical state during charging that would be mitigated by cessation of charging.