You could use a LiPo battery and a Power Module connected through "Power" labeled connector. This method allows to get readings of the battery voltage.

Notice that the power connector has attach two ADC channels in order to read battery level. If you don't use this connector, you could use the two middle pins to have analog voltage lectures for a sensor/device.

** Power connector **
 | .  .  .  .  .  . |
   |  |  |  |  |  |
       ch0 ch1

Warning: The range of input of the ADCs are 0~5v. Do not connect anything that exceeds this voltage.

The servo rail input can be used as a Power method. For this method the ESC needs to have BEC support.

You could use a standard 5v @2A microUSB charger to do it. Use the microUSB port as the image below:

Do not use this power method at the same time that the Power Module or ESC input. Your board or power source can be damaged.