This paper aims at comparing different optimisation techniques, for finding the charge and discharge schedule of a battery energy storage system (BESS) in a grid-connected microgrid. One of the techniques, based on linear programming (LP), targets to reduce the energy intake from the grid and the diesel generator present in the microgrid. The other technique based on dynamic programming (DP-I), aims towards developing a day-ahead schedule which ensures minimum operating cost of the microgrid throughout the day. The paper also proposes a modified charge/discharge cycle constrained dynamic programming technique with an objective similar to DP-I, but it also aims towards bringing down the number of charge/discharge cycles in a planning day. The effects of the battery schedules prepared from all the three strategies on the lifetime time of the battery, are also compared. This work uses an 192-hour model of aggregated seasonal data of solar, wind, and load demand, along with an aging model in predicting the lifetime of the battery. The proposed work is demonstrated in a 33-bus distribution network.