Replying to myself lol, but just in case anyone is curious or reviewing this in the future, I discovered LTspice doesnt allow the capital M for megaohms, and then converting to kiloOhms I entered the wrong value. 25.6MOhms is 25600kOhms. Now the simulation is working nicely and doesnt seem to care much about R4 (results are roughly the same from R4 50k to 800k).
I'm still insterested in how to determine R4 if anyone knows, but for now I think the solution is accepttable and Im going to order a PCB to test it.

I have been trying to get this LTspice to work. have also built a model from scratch. Just cannot get any sensible results. Can you upload your working model?

Mod: created a new thread.
Link to old thread.
https://forum.allaboutcircuits.com/...er-and-14s-lipo-batteries.205334/post-1966298

 

I have been trying to get this LTspice to work. have also built a model from scratch. Just cannot get any sensible results. Can you upload your working model?

Yes but I'm out of the house today. I'll try to remember to this evening

 

Super. I seem to get either 0v or a few tens of mV output, not matter what input I have, which is not what I get from the built circuit. I must have done something wrong!

 

Super. I seem to get either 0v or a few tens of mV output, not matter what input I have, which is not what I get from the built circuit. I must have done something wrong!

This version looks to be working. Hope it helps

 

Ah! Yes that is working for me.... thanks, thats brilliant. Now I will have to go and compare, and work out what I did wrong!
Many thanks!