Headset with microphone effect on smartphone battery life
Usually electret/condenser microphones require power to operate. These microphones are also called as capacitor microphones. There is a capacitor whose one plate will move as per the sound waves. This will cause a change in the capacitance which is equivalent to the sound waves.

In order for these microphones to work, power is required. Capacitors has rtto be charged to see the capacitance varying. These microphones are powered from the same audio line of the amplifier. If there is no power reaching the microphone, then it can't operate. Hence it draws small amount of current.

It is normal that these microphone consumes power. For any electric circuit to work, current is required. Each device you connect to your phone will consume power. Since the current consumed is 0.17mA, you won't notice a big difference in the battery life.