The electrified L9000 when released in October, 2014 had overvoltage protection built into the lock firmware. This over-voltage protection was removed in 2016 to accommodate the use of power supplies that had greater fluctuations in voltage that would exceed the recommended voltage of 24vdc (+10%). Over voltage (exceeding 31vdc) can permanently damage the lock. Therefore, the use of a varistor is now recommended.

A varistor is a semiconductor diode with resistance dependent on the applied voltage. It is used to prevent overvoltage to a circuit.