I literally complained about bait & switch tactics of websites yesterday on here. Sure, this isn't technically Bait & Switch. It's actually worse. BigBattery is using funds from a purchaser of a product they advertise to be "in stock". They have purchasing power with those funds. Websites are ripping consumers off daily now & these bigger ticket solar items are a perfect example.
Most websites have ZERO actual stock. They are a pass through shell site. Click, pay...funds transfer & your item ships from a distribution hub of a MASS Wholesaler. I write insurance & these shell sites are big business because you're just a marketing website shell advertising items in stock from a massive distribution center that every other website in your product category ships out of.
If I had to guess, you bought a product that was "technically" in stock in a distribution center, but a bulk of orders from all these pass through websites came through and websites with more buying power were shipped in the in stock product off the massive shelf.
The "restock" of that warehouse then is coming from the actual manufacturer & you get to wait until that truck hits the distributor. Even then, you're not really first in line.