Here is a pair of pedal based power meters made for serious cyclists in mind. The Favero Assioma UNO Power Meter Cycling Pedals have a sensor in the left pedal to measure leg power. They provide you with accurate data on your balance, torque efficiency, and smoothness as you ride your bike.
These power meter pedals are rechargeable and last up to 50 hours. They are smart enough to go to stand-by to conserve energy. With the companion app, you can calibrate the sensors, check battery charge level, and a whole lot more.