The batteries in EVs do degrade over time and so the range of the car declines - eg a car that started out with 200 miles will gradually drop and its value will drop accordingly - but even with a range of 50 miles it will satisfy some users for a local car so it will still have some value. As newer batteries and battery mgt systems are improved the speed of degradation should slow. In some cases one or more cells can fail completely which will result in a large sudden decline in range and possible charging problems - this is where it would be very expensive to replace the whole battery - in reality I would expect new repair businesses to be established which would repair batteries by replacing cells rather than the whole battery. It might not be as bad as it would appear today for future older EV values. Hybrids on the other hand....... will be exposed as the con of the 2020s.My view (and I an EQA on order) is that Mercedes hybrid and electric cars will be worth very little at 8 years / 100000 miles - because that is the Mercedes battery warranty limit. And I can't see how anyone is going to come up with a decent price aftermarket warranty for an 8 year old battery, so who will want to buy one? (especially as the automotive press gets hold of the issue in due course)
I don't know how long the warranty is on the OP's car, but I hope it us 8 years / 100k miles so that he has cover and keep an eye on resale values to know when to replace it without pain !