The battery pack on a Tesla Model S costs $16,000. The cost of an IC engine for an equivalent vehicle is about $3 to $4 thousand. The battery pack is warranted only for 50K miles. It -- just like an IC engine -- might last eight times as long or more. But then again, it may not. The "fear" is not an irrational one.
Having said that, though, it's worth pointing out that on *other* maintenance costs, a Tesla, at least, tends to outperform conventional vehicles.
Talk to Musk/Tesla about the warranty. The battery pack in a new Prius (plugin or not) is warrantied for 150,000 miles in states that have CA like emissions laws.
https://www.caranddriver.com/research/a31274277/prius-battery-life/ In NON-CA Emissions law sates, its 100,000 miles. Musk and Tesla offering crap like this is why it is MY OPINION that Musk/Tesla will fail when the other real automakers get their EV show on the road. A warranty is not necessarily, however, an indicator of when something will fail. New electronics, TVs, HTRs, etc, typically have a 1-year warranty but last much longer than that.
And besides, for someone like you, it is something that can be replaced without taking it to the dealer. Its not rocket science, and there is a market where used Hybrid batteries and cells can be bought and sold.
Something more you did not bother to check out before you posted??
I'll give you credit, though, pretty much all EVs are predicted to have significantly lower overall maintenance costs.