A cordless surgical device includes a modular battery, a radio-frequency signal generating assembly, a surgical handle and an interchangeable circuit casing. The RF signal generating assembly includes RF-signal-generating circuitry, a voltage-control circuit and an external output. The voltage circuit is configured to control an output of the RF-signal-generating circuitry. The handle is configured to support a bipolar end effector having jaws with bipolar contacts and a cutting blade disposed between the jaws. The handle includes leads operable to receive RF signals from the external output and defines an aseptically sealable battery-holding compartment configured to hold the battery. The circuit casing is configured to house the RF signal generating assembly and includes a securing connection adapted to couple the external output of the RF signal generating assembly to the leads. The external output is operable to impart RF signals to the handle when the circuit casing connects to the handle.