Energy-minimal setup with remote notifications and control


I'd like to replace my legacy wired system with konnected hardware.  I happen to also have a SmartThings hub, however using the hub is not optimal because I'd like the system to work during power outages.  That is hard to do with the SmartThings hub.  I cannot run wires between the alarm and the hub, so then I would need two battery-powered UPSs: one for the hub, the cable modem, and the WiFi AP; and another for the Konnected hardware.  Hub+modem+AP are fairly power-hungry.  Also I don't know if the cable ISP will keep working during an outage.

The alternative would be to connect the Konnected to a dedicated WiFi-LTE hotspot using an old cell phone and a Google Fi data-only SIM.  I expected the data usage of the Konnected system to be very low.  If I do this, I wonder if there's any service and software that supports it.  At the very least I will need a dynamic DNS, but it would be nicer to have a full-fledged service with notifications (when the alarm is triggered, or for other events) and the ability to turn the alarm on and off.

A 1/2-way solution would be to get a second SmartThings hub and connect that to the phone.  I haven't tried, but I imagine that SmartThings supports multiple hubs.  In the worst case I can pretend they are multiple houses.  That would not be too hard, but I still need to power the hub during outages.

Does anybody have suggestions for this?  Thanks!