High Amperage dc voltage regulator

[cat3rn]

I am trying to build a circuit that will do three things.

1. Must be able to disconnect the circuit if voltage drops below a certain voltage. i.e. 9 to 12 volts

2. Must be able to limit the voltage used to charge two separate batteries.

3. Must be able to handle up to 200 amps.

This is to be used in my car to keep the car from not being able to crank over when I play the stereo when the car is not running. Also because it is a Hybrid vehicle the main battery that is used to start the car becomes drained when it is left unused for 3 or more days.

I am not sure why but it probably is because the way it charges while driving around with the stereo on, not allowing it to fully charge.

So I would also need to protect each battery from being drained to the point where neither one will be able to start the car after I have done one or the other of the above things. That is why I want this circuit to cutoff any voltage drain at a certain point. I would also like to be able to keep the batteries from being overcharged. The circuit would have to stop the incoming voltage until a point where the batteries needed to be charged, say around 10 volts and then be able to shut off again when the batteries are fully charged.

I am not sure if this can be done or even if it makes sense so I am just asking to get an answer. If it can be would it be possible to draw out a schematic and a supply list of the parts I would need?