When you see information on batteries you often see their performance talked about as their Depth of Discharge or DOD. This is the percentage of battery capacity that can be used. For some batteries you can use 80 or 90% of their capacity but others only allow you to use 30%. It is very important to understand this when you are looking at the output of any battery.
You can have a range of batteries, all having 10 KW capacity but if one battery has a DOD of 80% where you would actually have 8KW of available storage another one might have a DOD of only 30% which means you would in fact only be able to use 3KW of storage. This means the lower the depth of discharge the more batteries you would need to achieve the same storage capacity.