The voltage my test setup was calculating looked wrong, then I realised that the sample calculation in the RAK Wireless forums wasn’t applicable to my setup.
I reassembled my RAK11200 WisBlock WiFi Module, RAK19001 WisBlock Base Board, RAK1901 WisBlock Temperature and Humidity Sensor, 1200mAH Lithium Polymer (LiPo) battery, SKU920100 Solar Board test setup, put a new 9V battery (I had forgotten to turn it off last-time) in my multimeter then collected some data. A=ReadValue(), C= ReadRatio(), E= measured battery voltage.
I updated the formula used to calculate the battery voltage and deployed the application
public static void Main()
{
Debug.WriteLine($"{DateTime.UtcNow:HH:mm:ss} devMobile.IoT.RAK.Wisblock.AzureIoTHub.RAK11200.PowerSleep starting");
Thread.Sleep(5000);
try
{
double batteryVoltage;
Configuration.SetPinFunction(Gpio.IO04, DeviceFunction.I2C1_DATA);
Configuration.SetPinFunction(Gpio.IO05, DeviceFunction.I2C1_CLOCK);
Debug.WriteLine($"{DateTime.UtcNow:HH:mm:ss} Battery voltage measurement");
// Configure Analog input (AIN0) port then read the "battery charge"
AdcController adcController = new AdcController();
using (AdcChannel batteryVoltageAdcChannel = adcController.OpenChannel(AdcControllerChannel))
{
batteryVoltage = batteryVoltageAdcChannel.ReadValue() / 723.7685;
Debug.WriteLine($" BatteryVoltage {batteryVoltage:F2}");
if (batteryVoltage < Config.BatteryVoltageBrownOutThreshold)
{
Sleep.EnableWakeupByTimer(Config.FailureRetryInterval);
Sleep.StartDeepSleep();
}
}
catch (Exception ex)
{
...
}
To test the accuracy of the voltage calculation I am going to run my setup on the office windowsill for a week regularly measuring the voltage. Then, turn the solar panel over (so the battery is not getting charged) and monitor the battery discharging until the RAK11200 WisBlock WiFi Module won’t connect to the network.
devMobile's blog 
hi!! did you test it? im doing a project with this and i would like to send the battery consumption to my dahsboard and i was wandering to see if there was an acurrate way to get it, thank you!