I bought a pair like this one. $40 each after a discount.
It doesn't have to be large. EVs have small 12V batteries. There is no engine to crank over. I haven't needed it for the EVs, but did start a Honda and a Hybrid Sonata. I don't recommend driving without one.
The tire kit is on Amazon. https://www.amazon.com/gp/aw/d/B07MR5FX8M
I started two cars with the booster last month: https://www.amazon.com/gp/aw/d/B07Z1D26CS