The performance and life of Li-ion batteries are susceptible to the operating temperature range. As the desired operating temperature is between 15-50°C the thermal management of high-density prismatic batteries requires cooling techniques with high heat transfer capability. Pulsating heat pipes (PHP) can dissipate large heat loads through a liquid-vapor phase change and slug-plug oscillations of the working fluid in the capillary channels. A flat plate pulsating heat pipe (FPPHP) is more suitable for cooling prismatic batteries as the capillary channels are machined on a flat plate. The working fluid predominantly governs the thermal performance and operating range of an FPPHP. Hence, Acetone- Water mixtures are tested as working fluid in FPPHP to maintain the battery's operating temperature range. Acetone can initiate oscillations at low heat inputs because of its large saturation pressure gradient, low boiling point, and latent heat. Water can delay working fluid dry-out at high heat inputs due to its large latent heat and specific heat capacity. Therefore, acetone-water binary mixtures can work over a wide range of heat fluxes. Most studies on PHP with binary mixtures were reported on a capillary tube PHP. To the best of our knowledge, there are no studies on an FPPHP with acetone-water mixtures, and the present work bridges this gap. In the present work, the thermal performance of an FPPHP with acetone-water mixtures is investigated experimentally. The closed loop FPPHP with 34 channels is made up of copper, and the channels are 180 mm long, 1.2 mm wide, and 1.2 mm deep. The length of the evaporator, adiabatic, and condenser sections are 65 mm, 50 mm, and 65 mm, respectively. The acetone-water binary mixtures used in the study are 3:1, 1.1, and 1:3. The thermal performance of the FPPHP is characterized by the total thermal resistance and the maximum evaporator temperature. The acetone-water mixtures performed better than the pure water over the entire heat range of 40 -160 W. Water has the highest thermal resistance and the worst-performing working fluid. The low saturation pressure gradient of water hindered the oscillations and resulted in the worst performance despite having high latent and specific heat. Pure acetone has the least thermal resistance among all working fluids until 80 W due to a high saturation pressure gradient and low boiling point, but dry-out occurs afterward. The early dry-out of pure acetone is due to low latent heat and specific heat. The water content in the acetone-water mixtures prevented early dry-out and increased the operating range of FPPHP because of its high latent and specific heat. The acetone content improved the oscillations in FPPHP because of its high saturation pressure gradient and low boiling point. The best-performing acetone-water mixture is the 3:1 mixture.