[Al Skierkiewicz]

Brian,
Measuring internal resistance takes some specialized gear to get it right. The 0.011 ohm specification is what is published for most of the batteries. It is however most often termed "internal impedance". For simple resistive loads, that is sufficient to use as a resistance in your calculatons. However, with complex loads like the PWM motor controllers and motors, the impedance would enter into more complex calculations.
The Battery Beak makes a quick calculation by switching in two resistive loads and making the calculation based on those readings. My examples all use worst case currents based on resistive loads.
Please understand that terminals, wire and connectors all will add to that resistance and the value is only valid on new, fully charged batteries. The one foot length of #6 wire allowed by FRC rules will add 0.001 ohms, the bettery terminals and Anderson connector will add another 0.002-0.004 ohms. So if you are measuring at the SB50, your reading of 0.018 ohms is accurate.