And cables, and a rack to hold them, and a tool to crimp those big huge cables, etc.
For professional installers, they can install these pretty easily, or install the more 'integrated' systems with a much, much larger margin for faster..
[0] https://www.currentconnected.com/product/eg4-ll-48v-100ah-se...
2. Financing. Most likely you are driving a EV financed by a bank. They've got the process so streamlined you can know within minutes if your 4-wheeled battery bank is coming home with you or not. Trying to get a house battery financed is such a convoluted mess. If it was advertised like a dealership, "Come down to Big Al's Battery Barn. We'll set you up with a 10kWh bank with 0% financing!", I imagine these things would fly off the shelf. Leading back to 1.
Standalone batteries will be in the low $200/kwh and DIY in the low $100s.