I prefer a "Voltage Correction Factor" that allows the "Battery Check" function to blink out 3.7 when the battery voltage range is between 3.70 V and 3.80 V (or as close as I can get to that).
I calibrate at 3.7 V since it is near the middle of the typical voltage range (instead of at the extreme low or high end which could cause unexpected inaccuracies at the end opposite from the calibrated end) and I usually have a stored battery at the exact voltage required for this method.
The available "Voltage Correction Factor" selections are:
1 Click for a -0.30 voltage offset
2 Clicks for a -0.25 voltage offset
3 Clicks for a -0.20 voltage offset
4 Clicks for a -0.15 voltage offset
5 Clicks for a -0.10 voltage offset
6 Clicks for a -0.05 voltage offset
7 Clicks for a 0.00 voltage offset
8 Clicks for a +0.05 voltage offset
9 Clicks for a +0.10 voltage offset
10 Clicks for a +0.15 voltage offset
12 Clicks for a +0.25 voltage offset
13 Clicks for a +0.30 voltage offset
Method for Setting the Anduril 2 "Voltage Correction Factor":
There will be two (adjacent) "Voltage Correction Factor" settings that allow the "Battery Check" function to blink out "3.7" for a "Battery charged to 3.73 V".
Choose the one that can be selected with the least amount of clicks.
After doing this, the blink out from the "Battery Check" function will change from 3.6 to 3.7 when the battery is between 3.68 V and 3.73 V, but you will not know the exact battery voltage where the change occurs without testing more batteries at different voltages and even if you did, you would not be able to get it much closer to 3.70 V since you can only change the voltage offset in 0.05 V increments. Also, when the "Battery Check" function now blinks out 3.7 the battery voltage range could be anywhere between "3.68 V to 3.78 V" and "3.73 V to 3.83 V".
You may wish to alter the battery voltage used with this method to suit your particular needs and preferences.
The "Voltage Correction Factor" and "Battery Check" function are detailed in forum member ToyKeeper's "Anduril 2 User Manual":
Explanation of Method used for Setting the Anduril 2 "Voltage Correction Factor"
Because the "Voltage Correction Factor" increment is 0.05 V and the "Battery Check" increment is 0.1 V (which is twice as large), there will be two (adjacent) "Voltage Correction Factor" increments that allow the "Battery Check" function to blink out "3.7" for a battery charged to 3.73 V.
Choose the "Voltage Correction Factor" increment that is selected by the least amount of clicks for a battery charged to 3.73 V, because that is the only choice which allows the "Battery Check" function to blink out "3.7" for both a battery charged to 3.73 V and a battery charged 0.05 V higher at 3.78 V.
It is unknown and not required to know exactly where a battery charged to 3.73 V falls within the "Voltage Correction Factor" increment selected by the least amount of clicks and since it could be at either the lower or upper increment boundary, all we know for sure is that the lowest voltage of this 0.05 V increment (where the blink out from the "Battery Check" function will change from "3.7" to "3.6") will be somewhere between 3.73 V and 3.68 V (where 3.68 V was calculated by subtracting the 0.05 V increment from 3.73 V).
A battery charged to either 3.73 V or 3.72 V works well for this method. Theoretically, a battery charged to 3.725 V would have been ideal, but my voltage meter only reads out to two decimal places at this voltage.
The easiest way to visualize the results from the "Voltage Correction Factor" is to construct (either in your mind or using paper and pen) two separate "number lines" (both to the same scale) with one using graduations of 0.1 V for the "Battery Check Number Line" and the other using graduations of 0.01 V for the "Actual Battery Voltage Number Line".
Orient the two number lines side by side (like an old style "Slide Rule") at a random (or chosen) alignment and then select and mark a specific battery voltage (in this case the voltage selected for the calibration battery) on the "Actual Battery Voltage Number Line".
Slide the "Actual Battery Voltage Number Line" along side the "Battery Check Number Line" in increments of 0.05 V to simulate and visualize different scenarios.
That's all I have to say about that "Voltage Correction Factor" - Forrest Gump.
But I'll reserve this post just in case I have more to say in the future, like maybe:
Perhaps the "Battery Check" function could be updated to allow "10H while using a battery charged to 3.70 V" to automatically set the "Voltage Correction Factor" (preferably aligned within ±0.01 V to the "Battery Check" function), but for safety's sake it would not change the "Voltage Correction Factor" by more than the currently allowed ±0.30 V from the factory default (to minimize any serious adverse effect on the Anduril 2.8 V low voltage protection) in case someone used a battery that was not charged at 3.70 V.
Disclaimer: I fully understand that the "Battery Check" function will never be very accurate due to hardware accuracy limitations and temperature compensation issues along with battery voltage variations during load and recovery, so voltage calibration is not that critical, but since I always do calibrate the voltage on my Anduril-2 lights, it has been an interesting brain teaser pondering about a quick and simple method to select the optimal "Voltage Correction Factor".