how to read the voltage of li-po battery?

[vivek khatri]

we make the tracking system. so, we want to measure the voltage of li-po battery (i am using nrf51 sensor tag with li-po battery), so, their is any circuitry or any API or function give me a voltage value. 

[Karl Ylvisaker]

Hello,

I see that you have tagged your post with both nRF51, nRF52840 and asset tracking ( nRF9160 ), but going by your text I will assume you mean nRF51.
As Patrick mentions, there are multiple forum posts on this matter already, such as this one. Please have a read-through of these, and let me know if you should encounter any issues or questions.

Best regards,
Karl