The increased adoption of renewable energy sources is reducing the overall inertial response capability of the modern electric power grid, which translates into larger frequency variation in both transient and pseudo-steady-state operation. Energy storage system (ESS) has the potential to play a significant role in regulating the frequency of more renewable electric power grid. This service is commonly known as frequency response or enhanced frequency response (EFR). Lithium-ion (Li-ion) battery is a popular choice as an ESS to provide EFR. However, EFR is very dynamic and the battery may have to provide high and fast response. This may accelerate the aging process of the battery. To overcome this issue, hybrid ESS (HESS) comprised of Li-ion battery and supercapacitor (SC) have been proposed in the literature. HESS typically works through power-sharing method (PSM). This work deals with the design of power sharing controllers able to enable the provision of EFR services from HESS. Keeping the battery lifetime in mind, proposed controllers employ a hybrid PSM by combining both proportional integral (PI) control and Fuzzy logic to maintain the battery state of charge (SOC) as close to the reference as possible while providing EFR. Results show that the lifetime of the Li-ion battery can be significantly extended by using the proposed controllers. However, this depends on the capacity of the SC that is used to support the Li-ion battery. Numerous simulation results are provided to demonstrate the suitability of the proposed controllers.