I assume they're talking about cobalt? That's the usual one.
There's about a billion cars in use worldwide -
source
Assuming they're all replaced by EVs, we need a billion battery packs, each of which contains about 18kg of cobalt -
source
That's 18 million tonnes of cobalt. Given that current reserves of cobalt are about half that -
source - there would seem to be a problem.
However...
All this assumes that :
No car batteries will be recycled, ever. Which isn't the case.
Batteries will continue to need this much cobalt. Which isn't the case.
We won't ever find new supplies of cobalt. Which is
absolutely not the case.
Without getting technical, for something to count as a
reserve, someone's evaluated pretty precisely how much material is there, in what quality, and has worked out that it can be extracted, processed and sold, using current technology and pricing, and proven that to various legal and financial standards. If you can't do every step of that, it's a
resource and doesn't count in the same way. Do your analysis, prove your working and resources become reserves. It's a costly and long winded process, and you don't do it till you need to. That's why we've always had 20 years reserves of oil as long as I can remember, and we probably always will.
The important point is that people tend to use resource and reserve as if they mean the same thing, and the same as 'total amount of stuff there is' - which is again, absolutely not the case
The Earths lithosphere - the layer of rock we live on, the crust - is about
0.003% cobalt, and it weighs about
23 000 *10^15 tonnes.
Do the sums, and there's over a billion times more cobalt than we've actually found. We're not going to run out.