Abstract: Secondary frequency regulation of thermal power units assisted by energy storage systems has the advantages of fast responsespeed and high tracking accuracy. However,improper power allocation can accelerate battery life degradation,resulting in increased operating cost and reduced economic benefit. Therefore,how to formulate a reasonable energy storage power allocation strategy to ensure frequency regulation performance while extending battery life and improving economic benefits has become a key issue that needs to be solved urgently. A mathematical model of energy storage lithium battery based on the second-order RC equivalent circuit was established firstly,andthe limited memory least squares recursive algorithm to identify the model parameters was then employed. Subsequently,three power allocation strategies such as proportion,difference and frequency were simulated and analyzed based on the joint frequency regulation model ofthermal storage. Finally,with the actual operational data from a 660 MW thermal power unit in Jiangsu,the effects of different strategies onsystem frequency regulation performance,battery life and economy were analyzed. The obtained results indicate that the proportion allocation strategy has the worst frequency regulation effect and accelerates the battery life decay. The difference allocation strategy performs wellin frequency regulation performance but has limited effect on improving battery life. The frequency allocation strategy can effectively reducethe battery replacement frequency and thus improve the overall economic benefit. Generally,the frequency allocation strategy can not onlyimprove the frequency regulation capability,but also maximize the battery life with optimized economic benefit,demonstrating significantapplication advantages in the secondary frequency regulation assisted by the energy storage systems.