Netgear Nighthawk, ac1900 C7100v. It is a modem router that supports voice. want a battery.

I bought this modem router because it supports voice.  I need a battery back up and this one has it except it didn't come with a battery.  Netgear doesn't know what battery it takes.  Amazon knows what the battery is but they say it doesn't have any batteries for it and doesn't know when they will be available.  How can Netgear sell a product with battery back up and then not provide a way to buy the battery.  The battery is PB022-100NAS just in case someone else wants to know.  So after spending considerable money for this modem I now have to buy a expensive UPC battery backup computer strip.  This doesn't make sense.  Does anyone have any ideas how I can buy a battery for this before I go further into debt for other equipment due to a modem that can't do what it is suppose to.  If I sound frustrated, you bet I am.

Thanks to anyone who can help with an idea or information of when I can get a battery or where.