What you are missing is home batteries have INSANE markups.

5kWh of battery cells at the moment run around $500. The rest of the cost of production is in the power electronics (probably around another $500).

It's why you can buy 4kwh worth of battery backups from Amazon for about $2k right now. Yet the same thing sold as a home battery backup costs $5k.

Lack of competition and likely low amount of sells is what's causing the margins to be so high.