Battery storage will play a crucial role in integrating variable renewable electricity generation into power systems, yet it is still uncertain how the location, scale and timing of storage deployment will affect its benefits. Here we improve a high-resolution power system model, SWITCH-China, to study the impact of different battery storage deployment strategies on carbon emissions and power system costs considering the location, scale and timing of the battery deployment. We investigate the effects of battery deployment strategies on the national electricity transmission and provincial coal-fired power generation. Utilizing supply side batteries constrained to only charge with co-located renewable energy can effectively smooth peak electricity transmission and reduce annual transmission costs. However, provincial analysis shows that supply side batteries will increase (decrease) coal-fired power generation in provinces with limited (abundant) renewable resources compared with batteries connected to the grid directly. Utilizing the Demand-side battery storage, which is connected to the demand load and can only discharge to local distribution grids, will induce the opposite effects for provincial coal-fired power generation and national transmission compared with grid-connected batteries. Battery storage deployment strategies should take provincial characteristics of solar radiation, wind resources and fossil fuel prices into consideration. Battery storage is potentially a game changer for renewable integration, but the timing, scale, and location of deployment to match the retirement of coal, renewable resources, the availability of transmission, and the characteristics of demand are key to maximizing its potential for power systems decarbonization.