A replacement battery for a Nissan LEAF (which I'll never need) costs little more than rebuilding the crappy transmission in my 2002 Honda Odyssey (which I sold for parts).

EVs are almost 10 times as efficient as an ICE. Therefore we will only need to replace a fraction of the energy currently being burned.  And there is plenty of excess capacity at night when most of us recharge our cars. An EV draws the same amount of power as a 9,000 BTU air conditioner or a portable heater. Utilities routinely replace and upgrade equipment with or without EVs.  This will happen gradually as EVs make up more of the fleet.