I've got a 20 milliohm sense resistor between the load\charger and battery. I'd like to get a A/D voltage with as much resolution as possible that is ratiometric. My A/D voltage reference is 2.5V. So, for example:

5Amps (Discharging) = 2.5V
0Amps = 1.25V
-5Amps (Charging) = 0V

Now, I know there are IC's designed specifically for this (Analog and Linear Tech) an example as such is:
http://www.linear.com/pc/produc...077,P36297

I'd like to perform this with just regular rail-to-rail opamps (such as a LM358). The opamp would be powered with 12.6VDC referenced to ground.

I just know there has to be circuit examples or application notes with an op-amp circuit out there, but I've been unable to find anything. I'd be interested if anybody has a link or ideas of how to implement this.

I've sort of twiddled around with simulating a differential amp with a 1.25V offset, but I think I'm missing something as the results were not as expected.

Thanks,
Tomas