Managing recharge power for implantable medical devices

This invention describes a way to safely charge batteries inside medical devices implanted in a patient's body. It works by having an external charger estimate how much energy is actually going into the battery versus how much is turning into heat in the patient's tissue. The claims narrow this down to a specific method of calculating the useful power stored in the battery by looking at its charge current and open-circuit voltage, separate from the heat generated by the battery's internal resistance. Based on these estimates, the charger can then adjust its power level to prevent the patient's tissue from getting too hot.