The cost of batteries is actually rising, now that manufacturing costs only make up ~25% of a battery's cost [1]. The remaining 75% is raw materials, dominated by the cathode and anode, which are having trouble keeping up with demand [2].
1. https://www.visualcapitalist.com/breaking-down-the-cost-of-a...
2. https://www.cnbc.com/2022/05/18/ev-battery-costs-set-to-spik...