The batteries also have an internal resistance that in case of large series connection
could be significant and could be necessary to take into account. The internal resistant
is a function of several factors among them are the design of the battery and thickness
of cells plates, materials, electrolytic fluid, and terminals design and materials.
Normally the internal resistance of a battery is just few ohms to fraction of an
How to Calculate the Internal Resistance of a Battery
Lest start by analyzing the battery internal and the load resistance circuit on
A and B below:
1- Measure the open circuit voltage of the battery with a high impedance meter, let
assume that it is 12.2 Volts, see figure A.
2- The equation that defines the close circuit voltage including the internal battery
resistance Rint and the voltage at the load Rload in figure B is:
Vtotal= VRint + VRload;
3-Choose a current for the which the internal resistance will be calculated, always
select a current that is safe for the battery current handling capability, lets say
10 amperes for this example.
VRload = Rload X IB ; where IB is battery current flowing in the resistors Rload