Could anyone recommend the ideal way to backup sum pumps in case of power outage and heavy rains?

Am considering a water-pressure driven sump pump system, that would run as long as the City supplies water $2,500.

Installing new sump pumps with battery backup would run about $1300 but batteries can run out of juice.

A generator is another option, but it runs on gas, has to be manually switched on and generates carbon monoxide and noise.  $1,000-$10,000.