This would work fine, but I'm not sure to what effect. To charge a 12v battery you need more than 12 volts (more like 15-16). Also, you'd only be able to charge one battery, but you would be pulling from four, so one of the batteries is going to die sooner.Sorry if this has already been discussed. I have a dc motor generator that produces 12v at 150 rpm. I'm hoping to mate this to an Etek style brushed motor that produces 8hp at 48v. This would be in a small lightweight trike for personal transportation. I would set it up almost recumbent bike style except the pedals would turn the generator at about 8 to 1 or 10 to 1 ratio. That would send power to the motor which would then turn the rear wheel. My question is would this generator motor be capable of handling the load placed on it? Would a blocking diode make any difference on this load? If not, I am prepared to accept plan B. Which is to insert four 12v batteries and use the pedal powered generator to simply charge them as I go. I would use some sort of slider throttle on the batteries for speed control. Sorry I don't have all the tech specs but would this work? It's not free energy if I'm pedaling.
It would also depend on how much amperage this generator makes at that speed. You'd need at least 2 A to get an effective charge going, and even then you're talking a slow trickle charge, extending range a bit more than charging it up for another trip.
It seems to me the best way to hook it up in parallel; that is, the system is only 48v, but when you're pedaling, the pull on the batteries is not as strong, some of the current is coming from you instead. This avoids unbalancing the pack, the higher voltage and amperage needed to charge a battery, and it increases efficiency too. Taking the pedal power and turning it directly into motion would be more effective still, but that engineering could be more difficult.