I want to measure the internal resistance of the batteries. I'll be using a Volt/Amp/Watt meter in series between the battery pack and the load resistor. I'll first read the no load voltage, then apply the load, and read the voltage and current. To calculate IR, I subtract loaded voltage from unloaded voltage and divide that by the amps. I can estimate the individual IRs by dividing the total IR by the number of cells. OK so far.

I used a 1 ohm 100 watt resistor on some 3 cell packs (12.6 volts fully charged). I waited about 10 seconds for the voltage to settle before taking the readings. The IR calculations are way too high. I assume I should use a much higher resistance?

My question is how much of a load to put on the battery and how long to leave it connected before taking the reading?

Jack