An eGPU is a battery driven, mobile Ground Power Unit. It is used to power the electrical onboard equipment of the aircraft while it is on the ground, getting prepared for the next flight.
At remote areas, a diesel GPU was the only option until the eGPU entered the scene. But diesel GPUs are noisy and polluting. Therefore, airports have a big incentive to replace those units with eGPUs. Actually, doing so means a reduction of more than 40% CO2 during a turnaround.
While airport operators and passengers benefit from no direct emissions and low noise levels close to the aircraft, the eGPU also ensures a short return on investment and minimal maintenance costs since there are no moving parts that are subject to wear and tear.
Read more about GPUs here.