battery life im unsure of, but worst case ill change to 1.5v lithiums
Opentherm does work on zones, i run my zones as rooms you can add upto 8 (iirc) trvs per room so opentherm would call for heat output from the boiler based on heat required for the rooms calling for it etc. Nest wouldnt work for me which is why i went for the drayton.
The trv's arnt mesh so require powered boosters if range is an issue but in my old cottage I didnt need any