Method for measuring internal resistance of batteries in WSN

In real Wireless Sensor Networks applications is very important to take into account the current battery state of health. A parameter that can provide significant information of the battery state is its internal resistance. For estimating the internal resistance, we assume a simple battery model composed of a source voltage and an internal resistor. This model is suitable for being implemented in low-cost motes with very limited computational capabilities. The procedure of estimating this value involves the acquisition of battery voltages and drained currents during the execution of a typical WSN application. We take advantage of the run-time execution of the program for measuring several voltages with different currents. Thus, the program measures the voltage and current when the system is in high power state (the radio is on) and in low power state (the radio is off). The method has been validated with real experiments with Telosb motes providing good results at different environmental conditions.