Over-discharge is one of the most damaging faults for Citycoco lithium batteries, which will directly trigger the battery management system (BMS) self-locking protection mechanism and cause the battery to fail to charge or discharge normally. When the Citycoco battery is ridden to complete power exhaustion or left idle for a long time leading to ultra-low voltage self-discharge, the single-cell voltage drops below the BMS safety threshold, and the system will lock the battery output and input functions to prevent further cell damage. At this time, the battery cannot be activated by ordinary charging methods, and a professional BMS reset operation is required to restore battery normal functions, which is a necessary maintenance skill for Citycoco users.

Before performing BMS reset after over-discharge, users need to confirm the battery over-discharge state and eliminate secondary faults. The typical manifestations of over-discharge locking are: the charger indicator remains green without charging response after connection, the scooter cannot be powered on, and the battery voltage detected by a multimeter is lower than the standard low-voltage limit (below 48V for 60V Citycoco batteries). Users should first check whether the battery terminals are oxidized or loose, whether the charging line is damaged, and ensure the storage environment is dry and ventilated to avoid short circuit faults caused by humidity. It is strictly forbidden to use high-power fast chargers for forced charging, which will cause battery bulging and even safety accidents.

The standard safe BMS reset method for over-discharged Citycoco batteries is trickle charging activation combined with static recovery. First, place the battery in a constant-temperature indoor environment (20–25°C) and let it stand for 2 to 3 hours to stabilize the internal cell voltage. Then use the original low-current standard charger to connect the battery for charging. In the early stage of reset activation, the charger may keep green for 30 to 60 minutes, which is a normal BMS pre-recovery process. Do not unplug the charger during this period; keep continuous trickle charging to allow the BMS to slowly identify the battery voltage and release the protection lock.

After the BMS is successfully reset, users need to conduct battery calibration and standardized maintenance to avoid repeated over-discharge locking. When the charger turns red officially, it means the protection lock is released and the battery enters normal charging state. Continue charging until full, then ride the scooter for a short distance to discharge power moderately, completing a full charge-discharge cycle to calibrate BMS data. In subsequent use, avoid deep discharge and long-term idle storage; charge the battery in time when the power is lower than 20%. For batteries that are repeatedly locked after reset, it indicates serious internal cell aging, and professional detection or replacement is recommended to ensure safe use.