We present an algorithm that maintains coverage of an open polyline patrolled by a team of robots. While previous work has focused on the uniformity of patrolling, we focus on ensuring the longevity of the system in the face of robot failures. A central control tower monitors the battery levels of the robots, and recalls them when they are low on power replacing them with fully charged robots. We compare two methods for replacement, both of which aim to keep coverage interruptions to a minimum. We present results obtained through physical experiments and simulations.