There's a difference between AC and DC charging. All current Tesla's accept 240 volt AC and there's no reason to expect that the semi won't either but with the such a giant battery pack 240V will simply not be fast enough. The 1000 volt is for DC fast charging. Tesla's current models use 350-375 volt battery packs. 1000 volt will just allow them to charge faster for DC fast charging, and more efficiently.