Russians deliberately don't attack telecom infrastructure now, because they did initially before discovering it was actually necessary for their own military comms.
Mobile routers can last 12 hours and handle a handful of connections, you can probably supplement them with a usb battery bank too.
Or if there is grid power within WiFi range it's not an issue. Or there may be more quiescent current models designed for IoT applications (like wind sensors in trees which may have poor signal coverage), I don't know