An electronic device can include a battery, a battery charger configured to receive power from an external power source and supply at least one of a charging current or a charging voltage to the battery, and a battery charger controller coupled to charger and configured to control the battery charger. More specifically, the battery charger controller may be configured to control the charger to supply a first AC signal as at least a part of the charging current or charging voltage supplied to the battery, measure a second AC signal associated with the first AC signal, and determine an impedance of the battery at a frequency of interest from the first and second AC signals. The electronic device can also or alternatively include a variable load that may be controlled to supply a first AC signal as at least part of the discharging current or discharging voltage of the battery.