**Re: eneloop vs. Kodak-> R_int Calculation**

The form (V2-V1)/(I2-I1) give the slope, so since

Rb=-slope, we get the equation that you have been using.

If you really want to capture the curvature, then you can use a quadratic equation that will fit a line through all the dots. A more complicated model

V=Compare that to V = Vo - Rb * ia *i^2+b* i+c

Using higher currents to determine Rb will result generally in larger values of Rb

Thanks PeAK - we were basically using the same equation(s) I only listed them so that others can be sure what Mr Happy and I were calculating.

However I prefer the version without using the R(load) - as there is no way I can measure the resistance accurately - mine is only a cheapo DMM which seems to show 0.6ohms when the leads are shorted on the 200ohm scale (the lowest) - readings for both 1 ohm resistors show 1.6 ohms - so one could say they are 1 ohm allowing for the 0.6 ohm offset....

- but that is really crude. Also the package rating/specs are 1 ohm +/- 10% so strictly speaking the resistor(s) used could be 0.9 to 1.1ohm - too much margin of error to use in the calcuations - using actual measured voltages and current(s) drawn probably has a better resolution on that cheapo DMM - even then it was liken to hitting a moving target - I just took the "best" measurements I could - it would probably be slightly different on another day/hour.....

Nevertheless I ended up with 3 sets of results for 0.5, 1, 2 ohm loads plus the open-circuit (no load) voltage which allowed 6 calculations for the internal resistance - and the general trend, not surprisingly, was that the internal resistance increased with increasing current draw (decreasing resistance)

this was enough to give reasonable "confidence" in the figures -

although there were slight variences -

there did not seem to be anything that stuck out to show possible major errors.

The increments for the resistive load were 0.5,1, and 2 ohms so pretty close to approximate the "curve" and in the common/practical range for flashlight usage (ie: in the range of about 0.6 to 2.4 Amps)

So the calculated internal resistances probably are good enough for an indication for both eneloops and Kodak Pre-Charged.

Not forgetting, of course, this is strictly limited to the samples of one of each of the batteries I used.