The cost of Lithium Ion battery capacity has dropped signfiicantly over time: 

https://ourworldindata.org/battery-price-decline

https://www.statista.com/statistics/883118/global-lithium-ion-battery-pack-costs/

I won't just be counting just Lithium Ion here, but I will reject any "battery' that has cells larger than a car, so as to avoid the inclusion of things like gravity batteries.

What will the$/kWh price for battery cells be at the end of 2030

 → What will the $/kWh price for battery cells be at the end of 2030