A wearable health monitoring device includes one or more sensors for sampling biometric parameters of various physiological conditions of the wearer. The device is powered by a variable energy source that has an energy level that changes during operation. A rechargeable battery loses charge as it powers the device. A solar cell or cells can be used to recharge, or maintain charge of the rechargeable battery, or at least provide a supplemental power source to relieve the burden on the rechargeable battery to power the device. In some circumstances, the available energy can become diminished, and the device adjusts the rate at which it performs biometric measurements in order to conserve energy.
