A voltage regulator system, comprising: a switched capacitor (SC) regulator that operates at a switching frequency and receives an input voltage; and a controller configured to control an operation of the SC regulator by adjusting the switching frequency of the SC regulator based on efficiency. In some embodiments, the switching frequency is swept to determine a best efficiency. In some embodiments, the switching frequency is swept at each of a plurality of values for the input voltage. In some embodiments, the system includes further one or more switches in series with the SC regulator. In some embodiments, the SC regulator includes an output terminal that is coupled to a battery.