I gotta reply.

Think about an electric motor running an alternator. If you use the alternator output to run the motor, it wont work because of a little word called "efficiency." If it did work, you would have perpetual motion.

Anyway, the motor takes more energy in than it puts out. The difference is consumed by friction and heat production. The alternator is the same.....more in than out. So we have to add more to the motor to get less from the alternator. Think of it as you working 8 hours for your wife to shop 8 hours....it aint gonna work.

Given you would have to add power, where would it come from? From the system you now have that is already running low.

What you might explore is a dual battery setup where the auxillary battery can be used to agument the system. The system would charge both batteries but the auxillary could supply a little extra power during a peak draw. A second battery is more compact than a motor/alternator too.