Collections of batteries are used to supply energy to a variety of applications. By utilizing the energy in such a collection efficiently, we can improve the lifetime over which energy can be supplied to the application. We say that the discharge of a collection of batteries is coordinated when, at the end of discharge, the difference in the remaining capacity of individual batteries is small. This paper presents a decision-maker based on a goal-seeking formulation that coordinates the discharge of a collection of batteries. This formulation allows us to use a simple battery model and simple decision-making algorithms. We present results from MATLAB simulations that demonstrate the performance of the decision-maker when energy is drawn out of the collection in three different discharge scenarios. The new decision-maker consistently improves the discharge efficiency obtained using scheduling methods. Our results show that when the discharge is coordinated, the lifetime of the collection is extended.