There comes a point late in the afternoon each day when we're out backpacking. Massey really has no endurance filter...its more of an on-off switch. Most times, that switch is stuck in the "on" position. So after a full day of chasing birds, bunnies, pika, marmots, lizards, and whatever else she thinks she should chase, the batteries need a recharge. While Terry and I filter water and make dinner, Massey chills. But is still on alert.