On 16 October 2014 12:48, John Gardner wrote: > ...Not so easy in practice it seems as the battery parameters are > constantly > changing. For example the voltage continues to drop when a load is > applied, so when do you take the measurements. > > It's not terribly difficult to measure V, A, & R at the same time > (More or less.). > > But it is not so straight forward. I can measure all those parameters at the same time and here are some real figures. 12.20V 800mA 15.3 ohm Load calc R =3D 15.25 12.17V 799mA 15.3 ohm load Calc R 15.23 12.15V 798mA 15.3 ohm load Calc R 15.22 Note: there are some errors introduced in this test, the test leads, the internal resistance of the current meter (which I seem unable to measure but this should given by the manufacturer) There is not much I can see that I can conclude about the internal of the Battery with these figures. What I need is the Open Circuit voltage of the battery, but when do I measure this, before the test, after the test, after it has been charged, after it has been charged and allowed to settle. Without and accurate or standard way to measure the open circuit voltage there is no way to calculate the voltage dropped across the internal resistor. The volt drop across the internal resistor is need (which we dont have) along with the current (which we have) to calculate its resistance. I must agree as has been mentioned, the model of a battery is more complicated than simply a voltage source in series with a resistor. But I am welcome to any suggestions on a method you have in mind. Justin --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .