gzt: Reliable in the sense that if the local power goes out your phone is powered by batteries at the exchange. It's not an issue for cities. Rural areas may have frequent power outages. I'll give them that point.
and yet all it takes is a single product such as:
https://www.pbtech.co.nz/product/UPSPSD1100/PowerShield-PSDCMIN1218-Mini-UPS-12VDC-1Amp-18Watt