battery level

Battery Display:

• When battery voltage is over N*3.3V,it will illuminate 1 block electricity quantity
  (note: N represents battery quantity)
• When battery voltage is over N*3.5V,it will illuminate 2 blocks electricity quantity
• When battery voltage is over N*3.7V,it will illuminate 3 blocks electricity quantity
• When battery voltage is over N*3.9V,it will illuminate 4 blocks electricity quantity.
• When battery voltage is less than N*3.3V,4 blocks display will be off; it represents battery
  is less than 3.3V,and you can charge the battery.