The large motor at full power requires 160 Charge (1:1) to work without draining a battery.
The medium motor at full power requires 40 Charge (1:1) to work without draining a battery.
The small motor at full power requires less than 5 Charge (1:1) to work without draining a battery.
(For the small motor, no value under 5 was mesured due to the generator engine stalling)
(Actually about 1.22 charge for the small motor Thanks to : https://gtm.steamproxy.vip/id/Ozyton )
(1:1 means no load or gearbox, see pictures)
The used setup. I lowered the engine RPM/Charge until the batteries started draining up for each engine and rounded the results upwards.




For a side note, I used *charge* levels directly and not the data from the batteries because they are based on % of the battery. 1.0 being 100% and so on. Basically, if you multiply the battery numerical output by 100, you make it into %. The logic gate I made for this guide tells me the % of the battery drained per second. Once it's at zero, it means my charger produces the exact/close amount used by the electric motor.

One solar cell in perfect conditions produces 0.001charge/s. Ouch.