Sennheiser SK50 with two AA batteries.

The graph below shows the comparative battery life of various AA batteries in a SK50 body pack transmitter.

The SK50 graph cuts off at 1.75 volts which is where the transmitter stops operating. The lines at 2.5 and 2 volts show where the battery sled indication changes from high to medium and medium to low respectively. The Energizer and Everactive batteries lasted 1.5 to 2 hours longer than the Duracell family of batteries.