The output power of the direct-drive wave energy conversion（DDWEC） system varies， which may not satisfy the requirements of the grid code for the wave generation integrated into power grids. To deal with this issue， the battery energy storage（BES） is applied to smooth the output power of the DDWEC. Two topologies of the BES applications， namely BES aggregated at the terminal of the wave farm（WF） and BES integrated to each individual DDWEC， are proposed. The controllers for the BES systems and the back-to-back converters of DDWEC are designed respectively. The fluctuation of the output power of the WF using BES is tested， and the effectiveness of the controllers proposed is demonstrated under the system disturbances， where the WF is connected to a single machine infinite bus system.