I have used a Harbor Freight 8500 Generator to Charge my Focus Electric at 7KW per hour. A generator is not advised generally as they are not USUALLY Pure Sine and may damage the charger. Inverter Generators are more expensive but like Pure Sine Inverters
are much more expensive and don't usually come in very high output. May be okay for temporary
emergency use. My Volt charger won't even engage unless on a pure sine.
I have used my 4000 watt RV generator countless times to charge my Zero DS ZF 6.5 without a trace of a problem. I always use one quick charger and the on-board charger at the same time when charging from gasoline.
BTW, I bring the DS ZF 6.5 on all my RV trips and sometimes I boondock far from any RV parks. It's really a great bike to carry on a cycle ramp on the hitch of the RV, as it's light enough and very easy to use the bike's electric motor to safely, slowly power itself up the ramp.
I never checked the waveshape, but I will the next time I run the RV generator. I have checked the frequency and voltage. It stays right at 60 hz and the voltage stays very close to 117 VAC under the ~26 amp load.
I expect mine to look better than that, but I would not expect even this distorted sinewave shown to cause any problems to a charger.
-Don- Reno, NV