An energy storage system may include battery packs, such that one terminal of the battery packs is electrically coupled to a resistor representative of an isolation resistance of the battery system. The system may include a semiconductor relay switch, a plurality of resistors configured to electrically couple to the battery packs via the semiconductor relay switch, a gain field-effect transistor (FET) configured to electrically short at least one resistor of the plurality of resistors, and a control system. The control system may send a first command to the semiconductor switch to close, acquire a first voltage waveform, send a second command to the semiconductor switch to open, send a third command to the gain FET to close, send a fourth command to the semiconductor switch to close, acquire a second voltage waveform, and determine the isolation resistance based on the first voltage waveform and the second voltage waveform.