How much does a 4 hour battery system cost? Figure ES-2 shows the overall capital cost for a 4-hour battery system based on those projections, with storage costs of $147/kWh, $243/kWh, and $339/kWh in 2035 and $108/kWh, $178/kWh, and $307/kWh in 2050 (values in 2024$).