Arrangement and method for determining the state of a battery based on a capacity of the battery

A battery arrangement configured to determine the state of a battery connected to a load and to a power supply unit, the battery arrangement comprising:

• a switch that is adapted to disconnect each of at least one first battery string and at least one second battery string in the battery individually from said load;
• and
• a control unit that is adapted to instruct said switch to disconnect said at least one first battery string from said load, and to instruct said power supply unit to reduce an output voltage to said load below a first threshold value, and to monitor the discharge of said at least one second battery string, and to determine the capacity of said at least one second battery string at least in part based on the monitoring of the discharge, and to detect whether a power from a utility line which is connected to said power supply unit is interrupted, and to instruct the switch to reconnect said at least one first battery string to said load if the power from said utility line to said power supply is interrupted.