Combined Heat and Power (CHP) systems are considered as a transitional solution towards zero carbon emissions in the next couple of decades. The current CHP systems are mainly controlled by thermal led strategy, that is, the electrical power generation depends on the thermal energy demand. The mismatch between the power generation and load demand leads to the deficient energy utilisation and economic loss. An innovative combined planning method is proposed in the paper to improve the economic gains of the CHP systems by integrating the lithium-ion battery storage system (LBSS). The paper focuses on the simultaneous optimisation of storage capacity design and operation strategy formulation of the LBSS subject to the variations of the load and power generation from CHP with consideration of LBSS degradation and cost, and Time-of-Use pricing structures. The new strategy is implemented and tested using the University of Warwick campus CHP system combined with the LBSS facilities. The results show that the method could improve the economic performance of CHP systems. The developed method is applicable to any CHP systems optimisation with integrated LBSS.