We examine the impact of batteries on security of the electricity supply and achieving renewable energy expansion. For this purpose, we develop an electricity market model that enables the simulation of batteries as a dynamic, economic-driven investment option. We present six policy scenarios in which batteries are utilised as an option that is subsidised by the government to secure electricity supply and engender renewable energy expansion. For each scenario, we simulate and analyse the amount of renewable energy produced, the electricity supply from batteries, total CO2 emissions and the requisite subsidies and external costs for achieving security of supply. Our simulations, based on empirical data, indicate that, in a free market, battery investments are not profitable for private investors. On the other hand, these six policy scenarios show that by subsidizing investments in batteries governments could ensure a secure electricity supply as well as ongoing renewable energy expansion. Comparisons to comparable policy scenarios that do not adopt batteries indicate that the total sum of government subsidies and external costs is up to 36% lower as a consequence of utilizing batteries.