These work really well for that task. Can power a cable modem and a small edgerouter-x using a y-cable. https://www.ebay.com/itm/Belkin-Residential-Gateway-Bat

These work really well for that task. Can power a cable modem and a small edgerouter-x using a y-cable. https://www.ebay.com/itm/Belkin-Residential-Gateway-Battery-Backup-REV-B-w-Battery-BU3DC001-12V/274684107792?epid=1600149188&hash=item3ff472dc10:g:fqAAAOSwuuFgFJzX https://www.ebay.com/itm/Belkin-Residential-Gateway-Battery-...