[fulafel]

Helicopter glide property is important because most are single engine. You could easily put several independent motor + battery partitions in this one.

[FabHK]

Indeed. The 18 rotors in two concentric circles (6 in the inner, 2 x 6 in the outer) are each driven by an independent engine, and they're operated by many power trains that supply rotors on opposite sides. So, if a rotor fails (or actually up to 4), no prob, still controllable for expedient landing. If a power train fails, same.

[devdoomari]

but then, wouldn't fuel efficiency go down?

[fulafel]

This is electric, the batteries are already just big bunches of small cells. Partitioning those won't appreciably affect battery performance.