A method of testing a rechargeable battery (4) connected to a DC bus (5) of a converter (11) of a power supply system (10) including a control system (12) for controlling power transfer between a power source (2), the rechargeable battery (4), and a load (3) connected to the DC bus (5) is provided. The method includes: setting a test discharge current (I4d) and a test end voltage (Vend) for the rechargeable battery (4) to be used during the test; at a first point in time (T0), starting a test run measuring a current (I4) from the rechargeable battery (4) and a voltage (V4) over the rechargeable battery (4); at a second point in time (Tend), when the V4 becomes equal to the Vend, terminating the test run; and registering the time period elapsed between T0 and Tend as a measure of the status of the rechargeable battery (4).