In practice, there are two main usages of the battery in home: reducing electricity energy cost by utilizing time-varying electricity energy price and enhancing privacy by concealing the electricity energy usage pattern of appliances. By operating the battery such that it is charged/discharged during periods with low/high prices, we can reduce the electricity energy cost. On the other hand, by operating the battery such that the electricity usage pattern can be significantly changed from the original usage pattern of appliances, we can protect user's privacy. However, those two operations are not complement with each other and there exists a trade-off between reducing cost and enhancing privacy. In this paper, we study this issue. To consider both cost and privacy in a unified way, we first define cost metric and privacy metric that should be minimized. Then, we define an overall metric as a weighted sum of the two metrics to study the trade-off between them. We formulate and solve an optimization problem that aims at minimizing the overall metric. Finally, through numerical results, we study and discuss the usage of the battery for reducing cost and enhancing privacy.