A Mercedes EQC 300 BEV came in with a sudden range reduction after sitting idle. Investigation revealed the dual-battery pack had severely unbalanced state-of-charge (10% vs 95%) due to a BMS software glitch. The dealer rebalancing procedure failed, so the mechanic manually charged the first battery and overwrote the faulty BMS module's memory with data from a known-good unit, clearing the error. The case highlights how deeply software-dependent modern EV battery systems are, and how the industry's default response is full module replacement rather than repair.
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