Drones/$ have an internal buffer of 100,000 FE (Forge Energy). Using this widget, you can import energy from an energy-providing block (e.g. a Thermal Expansion Energy Cell/$ or Immersive Engineering Capacitor/$) to the drone's internal storage.
Despite its name, this widget imports FE (Forge Energy), not RF (Redstone Flux). The name is historical./$

I've got the power/$