Wife Extender and Continued use even during power outages

Has anyone gotten or used the wife extender with the 4 hour batter pack in case of loss of power or network issues? They are trying to sell me on $7.38 per month plus $50.00 deposit.  My thoughts are why should I pay "insurance " on a service that should always be working.  Im not going to lie. Im not happy with Cox and have been actively searching for another provider. Any help would be appreciated.