I like the idea of a modular battery such as Sungrow SBR series for the ability to scale up:

https://www.acsolarwarehouse.com/news/sungrow-battery-and-hy...

Each module is 3.2kWh. Can start with a small stack of 3 modules (9.6kWh), knowing this can be trivially upgraded 2.6x later without blowing out the cost.