I'm still working all this out so hope 'Tutorial' is the right tag for this thread! Hopefully it helps or inspires someone anyway.

On Mobula7 I run 1s and 2s and like my X Lite to read out the low voltage warning since I often get carried away flying and forget to check the OSD until it's blinking like crazy!
I also plan to fly 3s and 4s on my micro.

I followed a few guides and had the audible alerts working well for 1s.  There are lots of ways to do this!
I then created a duplicate model and updated the rules for 2s.  However, changing models on the TX was a pain and easy to forget when changing cells on the model, so I thought of a neater way to do it.

I looked around and can't find this documented anywhere, so for anyone who runs packs with different cell count and likes the telemetry call out, here's my way to do. If you have any suggestions to improve it, let me know, but this works very well for me for now!

This is for Open TX, I'm running an FrSky X-Lite.

First, the assumptions on voltages for my HV LiPos.
1s - start at 4.35 max, end at 2.8 min
2s  - starts at 8.7 max to 5.6 min
You can see that they don't ever overlap, so the voltage falls into one range or another.  Unfortunately this doesn't work for 3s to 4s since the voltage ranges overalap, but would work 4s to 6s.  I think you could use STICKY to set a condition based on voltage ranges on arm if the voltages overlap.

To start with set up logical switches on your TX

Logical switches

L01 a<x VFAS 3.2V L05
L02 a<x VFAS 2.9V L05
L03 a<x VFAS 6.4V L06
L04 a<x VFAS 5.8V L06
L05 a<x VFAS 5.0V SC(down)
L06 a>x VFAS 5.0V SC(down)

where SC(down) is my arm switch position.  This means the logical switches are only on when the quad armed, which stops the TX squawking away when there's no LiPo connected to the model or when you run down the LiPo and disarm.

L05 is active when the quad is armed and VFAS is under 5V, therefore it's a 1s.
L06 is active when the quad is armed and VFAS is over 5V, therefore it's a 2s.
I also have a 2 second delay on the first 4.  L05/L06 VFAS check have a 4 second delay on there to allow the VFAS reading to stabilise when plugging in and arming.

When L05 is active (1s)
L01 is my low voltage warning, which triggers the special function below
L02 is my critical warning, again, see below.

Similar for L03 and L04 when L06 is active (2s).

If you only want one level of warning you can do away with L01 and L03 or L02 and L04.

Now the switches kick in, you need to decide what action to perform

Special Functions

L01 Play Val VFAS
L02 Play Track batcrt 6
L02 Haptic 3 2
L03 Play Val VFAS
L04 Play Track batcrt 6
[i]L04 Haptic 3 2

[/i]When a 1s hits 3.2V, switch L01 is active and the TX reads out the VFAS.
When it drops to 2.9V, L02 is active, the TX calls out "battery critical" on repeat every 6 seconds and triggers the haptic.  Hard to ignore!
Likewise for L03 and L04 for 2s.

So there you have it - how I tell between 1s and 2s without touching the TX.  Hope it's useful.  Got a better way, or a solution for 3s/4s? Let me know!

You can do it way simpler than this by using the average cell voltage rather than the total battery voltage. Then you don't have to worry about how many cells a LiPo has or what the min and max voltages should be based on the cell count of the LiPo. Voodoo previously posted that suggestion so I'll try to find the post.

Found it. Voodoo made the original suggestion to use average cell voltage HERE. You need to use the A4 sensor which is for average cell voltage rather than the VFAS sensor which is for total battery voltage. I then suggested an implementation HERE.

Also, take a look at Oscar's article linked below if you want to take it a step further, again substituting VFAS for A4 where referenced, and using 3.5V instead of 14V as the minimum voltage in any checks...

https://oscarliang.com/taranis-logical-switches-voltage-alarm