Q: Why this mod?
A: With very few moving parts, I felt that cogs were not an appropriate ingredient for this machine;
Also, the Roboport holds a charge (100 MJ), so using batteries in its recipe makes sense.
The way the graphics look also suggests that drones are inductively charged by the Roboport's "antennas" instead of physically connecting

Q: How does it change game balance?
A: It is a cheaper in iron and copper, but significantly more expensive in oil and energy required to make it.