url to purchase Pace 5268AC internal battery

I don't know of any such link.  I gave it the "old college try" and came up dry.  PACE shows such a battery on their site, if you know where to look, but you can't actually order it.  If you'd like to see that page, here it is:

http://www.pace.com/americas/5268ac-battery

PACE provides no purchase link (they're really not set up to sell to consumers, they want to sell to providers).  The part numbers on the battery image is useless, as is the contents of the QR code.

AT&T at best gives you a link to the PACE website where you can't even search for this battery.

My best recommendation at this point is that you go purchase a standard UPS that can give at least 10W for as long as you want the Gateway to stay alive.

Thanks for the quick reply JefferMC.  Do you know if this http://www.belkin.com/us/gatewaybattery/ unit work with the pace 5268ac?

I do not know, but I would be concerned that they may not:  I think that there was a specialized cord to plug the PACE 3600/3800/3801 into one of these, so these may have a weird outlet that you cannot plug the 5268ac into.

I was thinking something more conventional.

It's a crock that AT&T no longer provides a battery with their Uverse routers. I found that out when I had to have my old router (which came with a battery) replaced a few weeks ago. The battery costs $39.99. For $16 more I found this on Amazon, APC Back-UPS 600VA UPS Battery Backup & Surge Protector with USB Charging Port (BE600M1). It has 15 times more reserve power and a whole lot more versatility.

pace 5268 Gateway 8 battery pack number is on the Arris website sku # is 0990857

https://shop.surfboard.com/pace-5268ac-gateway-8-hour-battery-sku-239-0990857/