Since getting an iPad 3 with LTE earlier this year, I have noticed that the battery runs down much faster than my old Wifi only iPad. It seems likely this is caused by the iPad's constantly checking with the cell tower, GPS, and other services. With the iPad in ready mode, the battery runs down about 10% or more per day.
So I was thinking, there must be an app I can use to save battery life. Then it struck me, what about Airplane Mode. The Airplane Mode setting turns off all communication systems on the device (Wifi, 4G, GPS). So last night, I turned on Airplane Mode and left my iPad in standby. This morning, the device only had lost 2% of its charge.
So it seems like to me, the power saver mode is built in already. :)