You have small battery that can power heli at full power for about 10 minutes.
Even a R22 according to RHC needs about 60-70kW to maintain level flight at cruise speed. To deliver that for 10 minutes you need at least a 10,000Wh battery - about 200 times the capacity of a big laptop battery, or 20 car batteries. For a R22. 10 minutes.
Thats why the CB300 demonstrator can fly only for 15 minutes.
1. No gearbox needed, direct drive on the shaft. Weight savings, reliability improvements.
2. Brushless motors give more power per weight than any other engine (easily about 8-10Kw/kg - beat that gas turbines), which saves weight further.
Saves weight further? The Gen/Electric Motor/battery are replacing a gearbox, so weight is only saved if they are lighter than the GB.
The turbine is still needed.
Also, what would a brushless motor look like that can deliver, say, 200kW at 400RPM (for main rotor direct drive of a 5 seat helicopter), and would it really be light?
And imagine the battery for THAT.
4. Brushless motors are pretty much only limited by bearing life, so maintenance should become very cheap.
only the gearboxes are replaced in your example, the turbine is still there.
... no altitude penalties, no shock cooling, no performance losses from tail, no LTE, etc.
8. Much less noisy.
Why no altitude penalties? Again, the turbine is still there and required. Same with the noise.
An all electric helicopter would be a great thing for many reasons - but, given the poor energy efficiency of rotary wing flight in general, and the weight problems that come with it, I believe helicopters will be amongst the last vehicles on earth to be succesfully converted to battery power. And that will happen only after some massive breakthroughs in battery technology.