Don't waste your money. In most areas they do not meet the plumbing code unless you have an RPZ installed with it. Plus you are wasting good potable water to pump out ground water. Buy a Basement Watchdog "Big Dog" or get a Sump Pro system. Here is from another post on the subject of which backup sump pump system to install.
This is a repost of my response to another question about backup pumps and primary pumps. http://www.terrylove.com/forums/showthread.php?t=29509
The Basement Watchdog battery back up pump is a good decent system, their primary pump that they are selling in the combo system is junk though. The Basement watchdog system you want to go with is the Big Dog, do not go with the smaller systems. The smaller systems require you to manually test the pump to ensure it has not frozen on you. Where the Big Dog, will auto test itself and sound an alarm if there is an issue with the back up pump.
Now professional offered battery back up systems the PHCC Pro -2400 is a very good system it is made by Glentronics same people that make the Basement Watchdog systems and has all the same features as the Big Dog plus more.
Another system I really like uses two primary pumps like a pair of hydromatic D-A-1 or a pair of Zoeller M-53 The system is called a Sump Pro it uses a pair of marine batteries to run your pumps A/C pumps when the power goes out. It also alternates each pump each time the pump pit fills up so this way they both get worked out (pumps that do not run freeze up).
AS for a primary pump I sell Zoeller and Hydromatic pumps. A Zoeller M-53, or a hydromatic D-A-1 will work nicely for you