A battery charging circuit can produce a pulsed charging current to charge a battery. During charging, without disconnecting the pulsed charging current from the battery, EIS measurements can be made. In other words, the pulsed charging current can serve double-duty, for battery charging and as a drive signal for the EIS measurements. The EIS measurements can be used to alter parameters of the pulsed charging current to improve battery life. In some instances, the parameters of the pulsed charging current can be momentarily changed for the purpose of making the EIS measurements, and then restored subsequent to making the measurements to parameters suitable for battery charging.