Batter drain

[jessesung]

Borrowing the template from Garmin addon. :)

• How big drain do you get on your watch model?
  Gear Fit 2: 35%~100%. Sometimes I wake up from a 6-hour or so sleep and find the watch is already off.

• How big a drain is acceptable for you?
  It's always better to have a lower number. But giving the poor battery life of Gear Fit 2, 20%~25% would be acceptable.

• What might be the causes of the drain?
  Not sure, but I would guess bluetooth transmission plays a big role in this.

• What might be done to lower it?
  With a quick glance of SleepAsAndroidGearFitService, I'm wondering if it would help by enlarging SAMPLING_TIME_SEC, MAX_BUFFER_LENGTH, and batch_size?