Battery backup for Slate AXT1800?

Hi, my area gets power outages often lasting up to an hour each time, but I just want to keep my Slate AXT1800 always online. My laptops and devices are already battery powered, so the only problem is keeping network online. I don’t need a crazy expensive powerful standby UPS battery backup because this is just for the router and nothing else plugged into it. The power specifications on the router is unusual (USB Type-C 5V/4A). I will keep the battery plugged in the outlet at all times, so make sure it’s appropriate for this usage and won’t cause a fire or kill the battery. What do you guys recommend for this?