Exemplary methods and systems for charging a battery in a power management unit include a power regulator having an input power supply and a processor that regulates a charging rate of the battery based on measured parameters of the power regulator and the battery. The processor is programmed to perform exemplary methods that include receiving an output voltage signal and a battery temperature signal from the power regulator, and comparing the output voltage to a first threshold to determine a charge level of the battery. An exemplary method includes selecting a charging mode based on the comparison, and sending a first control signal to the power regulator to adjust a charging rate of the battery based on the battery temperature.