Did the Infinite Battery stop selling batteries? I get an error 404 message when trying to access the store page for the past week.
Google AI tells me, for what it’s worth, that whilst DIY kits are still available they have changed their primary business model to bulk commercial supply. I’m not entirely surprised as that has to be where the major business is conducted. All parts are still in Shopify and availablity but complete kits aren’t listed. It may be you will have to contact them personally to place a single order for a kit.
Looks like the website was updated, it does indeed look like they stopped selling to individuals unfortunately.