The top of the line LiFePo4 units do have blue tooth monitors integrated. At least some of the monitors do a state of charge.
The exact mechanism for SOC has never been made clear in any of the reading I've done. I do not think that it is necessarily voltage based--because the very best voltage based unit is the Smart Gauge--and it does not work with LiFePo4. That is speculation on my part. Coulomb counting? Maybe.
There are some batteries that tell porkies about their bms--saying it does have a cold weather disconnect--when nothing of the sort is inside the box.
If I were not a cold weather camper LI would be worth considering. But I'm not, and I'm no longer full time. SiO2 fit me like a glove. I'm set up to fit seven of them.
