In this work, we present some of the first experimental results along with simulation results obtained in developing and testing a novel dual-piston free-piston engine generator (FPEG), designed for electric- vehicle (EV) range-extender or hybrid powertrain applications. The benefits of a high-efficiency, compact and lightweight design of the proposed range-extender are presented. The technical details and experimental set-up of a two-cylinder prototype and its instrumentation are also outlined. Results are presented for simulation and recent test programmes carried out across both 2-stroke and 4-stroke operational modes. The methods associated with engine control are detailed alongside key post-processed engine characteristics.