decades. Every single announcement has been a grab for more grant money or investment. None of them have made it to market. We're still using basically the same lithium ion batteries we were using 20+ years ago.
If anyone has a real breakthrough that will allow them to deliver, we probably won't hear about it. They're going to keep in hush as long as possible while they secure their patents and arrange for manufacturing.
I'm not giving credence to any battery tech breakthrough announcements unless they promise manufacturing will commence within 6 months.