Battery internal resistance is when the current through the battery internal resistance. It includes ohm internal resistance and polarization resistance and polarization resistance internal resistance and concentration polarization and electrochemical polarization resistance. Due to the existence of internal resistance, the voltage of the battery is always less than the EMF of the battery or open circuit voltage. The internal resistance of the battery is not a constant, changing over time in a charge/discharge process (getting bigger), this is because the composition of the active substance, concentration and temperature of the electrolyte is in constant change. Ohm internal resistance to comply with Ohm's law, polarization resistance increases with increasing current density, but not linear. Often increases with the increasing current density.
Internal resistance is an important index to determine battery performance, it directly affects the working voltage of the battery, current, output power and power, battery, and its internal resistance, the smaller the better.