The shipping industry is facing increasing pressure to cut emissions. Diesel-electric hybrid or fully electrical propulsion systems can offer significant savings in fuel consumption and reduce emissions. However, the use of energy storage battery systems on board vessels is introducing new fire hazards and advice on suitable fire extinguishing systems and agents is desired. In a series of tests, both total compartment application water spray and water mist systems and direct injection (using several different agents) into the module were evaluated in fire tests conducted to compare different fire extinguishing approaches for a fire in a battery cell. A test compartment was constructed to simulate a battery room and a commercially available lithium-ion (Li-ion) battery cell was positioned inside a cubic box that mimicked a battery module. By heating the battery cell, combustible gases were generated, and these gases were ignited by a pilot flame inside the simulated battery module. The tests indicated that fire extinguishment of a battery cell fire inside a battery module is unlikely when using total compartment water spray or water mist fire protection systems. The water droplets are simply not able to penetrate the battery module and reach to the seat of the fire. Direct injection of the fire extinguishing agent inside the battery module is necessary. The tests also showed that agents such as water and low-expansion foam, with a high heat capacity, provide rapid cooling and fire extinguishment. The reduced water surface tension associated with low-expansion foam may improve the possibilities for water penetration whilst agents with a high viscosity may not be able to spread to the seat of the fire. Agents with less heat capacity, such as high-expansion foam and nitrogen gas, provide less cooling but fire extinguishment can still be achieved if designed correctly.