Also, 2 battery systems are exactly like 1 battery systems in those trucks. They are wired in circuit, so not 24V. Only 12V. It should start fine w one battery charged. It is extremely unlikely that both batteries "went bad" in that new truck. Something is draining it or he has a charging failure. The truck is under full warrantee if it's a 2017 or '18, just have it towed to the dealer and say, "fix it."
