My Correction #3
My bad. The batteries are expensive...$30!
On page 5 of the PDF version for my statement dated Apr 14, 2018-May 13, 2018:
"...you may order backup batteries from Cox by call (855) 324-7700 or visiting a Cox Solution Store. The cost for an 8-hour battery from Cox currently is $29.99, but subject to change."
"The Cox battery is warranted for one year."
"The battery offered by Cox is designed to fit directly into your specific telephone modem and may not be available at retail stores."
Also on the PDF, Cox repeatedly warns me to purchase "additional" batteries...at $29.99 mind you...as "reserve backup batteries."