Here's a circuit I banged out that might be able to help you.
It has a small current sensing resistor in series with the battery and circuit breaker. The voltage across the resistor, which is proportional to the battery current, is determined and amplified by a difference amplifier circuit that has a gain of 25, which allows the 1 milliohm resistor to fill the available range on the A/D input. (200A through the circuit corresponds to 255 A/D counts). And the wheel on the bus goes round and round.
You might want to throw on an output filter to remove the PWM ripple, and perhaps another gain stage to fine tune the circuit's range, but it should work reasonably well now.
Please note that Digikey doesn't have any 1 milliohm resistors that can handle enough power to work here - so you have to 'make' your 1 milliohm resistor from five 5mOhm precision resistors, or ten 10mOhm precision resistors (in parallel). Five of
these would be able to handle 24W continuously, which is short of the 40W required for the anticipated 200A spikes, but I think they would hold up in practice, because the average power dissapated would be well below 24W.
If you have any questions, let me know. I know that I didn't document the image too well, but it shouldn't be too hard to get the general idea.