Battery internal resistance measurement is a reliable procedure for battery condition assessment that is done within seconds. Combined with cell voltage and inter-cell connection resistance measurement, the test determines the state of health of batteries.
Internal resistance represents the battery’s limiting factor to deliver the required current and/or supply the required energy. High internal resistance results in increased heat generation in the battery under load, i.e unwanted energy loss. Furthermore, high resistance implies a higher voltage drop on the loaded battery. This will speed up reaching the battery cut-off voltage and triggering an early shutdown.
Most important of all, high resistance will reduce the amount of energy the battery can supply within it’s operating voltage. As a result of that, the battery capacity will be reduced.
Although internal resistance measurement does not determine battery capacity, it is a reliable parameter indicating aging pace. A user can compare old with the new measured values to keep track of changing trends.
Since battery resistance is temperature and state-of-charge dependent, measurements should always be taken under the same conditions of temperature and charge level.