Hanoi and several northern provinces have recently experienced continuous heavy rains, leading to widespread street flooding after storms. Many vehicles, including electric ones, had to navigate these inundated areas. While some owners believe EVs are "immune" to water due to the absence of gasoline engines or exhaust pipes, traversing floodwaters can severely damage the electrical system and battery if not detected promptly.

A 5-seat car reverses to avoid a deeply flooded section in Hanoi, 7/10. *Dinh Tung*

Slow charging or charging errors

One of the most apparent signs of water damage in an EV is slow charging or error messages during the charging process. When an EV travels through floodwaters, dirty water can infiltrate the charging port or battery compartment. This intrusion can trigger the battery management system (BMS) to automatically shut down for protection. Owners might then observe intermittent charging or error notifications. In some cases, vehicles may charge, but the process takes significantly longer than normal.

Attempting to continue charging could lead to current leakage, short circuits, or damage to the charger itself. The proper response is to immediately disconnect the charger, thoroughly dry all charging components, or allow them to air dry for approximately one day. Following this, the vehicle should be taken to an authorized service center for a comprehensive inspection.

Reduced power and rapid battery drain

Following exposure to water, an EV might exhibit a noticeable decrease in performance, even with a full battery. This can manifest as sluggish acceleration or an inability to reach higher speeds. These symptoms indicate that water has infiltrated some battery cells or the power controller, resulting in unstable output voltage.

Although EV lithium batteries are designed to be waterproof, moisture can still penetrate if the waterproof seal is compromised or the vehicle remains submerged in floodwaters for an extended period. This humidity increases internal resistance, which causes chemical corrosion and voltage imbalances among the cells. Consequently, the battery weakens and drains more rapidly. When some battery cells experience reduced voltage, the battery management system (BMS) must reduce the overall power output to protect the system, leading to a noticeable decrease in the vehicle's acceleration.

Rapid battery drain is often accompanied by a reduced driving range per charge compared to pre-flood conditions, or a sudden drop in the battery gauge during strong acceleration. Some vehicles may also automatically limit their speed to reduce the load on the battery pack. Continued use in this compromised state risks battery swelling, electrical leakage, or even explosion in severe cases.

Therefore, if an EV owner notices diminished power or unusually fast battery drain after driving through a flooded area, they should immediately cease operation, refrain from charging, and take the vehicle to a technical center. There, technicians can inspect the voltage of each cell and assess the insulation of the battery pack.

Burning smells, hissing, and unusual noises

Some EVs may emit a burning smell or produce hissing or rattling sounds during acceleration after traversing flooded areas. These phenomena often signal current leakage, partial discharge, or localized overheating in exposed electrical components or water-infiltrated zones. Examples include: connectors, charging ports, wiring, motor coils, or even the surface of battery cells.

Moisture-damaged insulation layers can lead to electrical arcing, producing small sparks accompanied by crackling or popping sounds. These sparks and leakage currents generate heat, which can char plastic materials, insulation, or adhesives. This charring then emits burning smells reminiscent of scorched plastic, wood, or metal.

Upon detecting any unusual smells or noises, owners should immediately disconnect the power to prevent heat from spreading to the battery. Subsequently, the vehicle must be taken to an authorized service center for a comprehensive system inspection.

A motorbike navigates a flooded area in Hanoi, 26/8. *Duc Dong*

Abnormal screen and button operation

Beyond major electrical faults, water can also infiltrate button clusters or the control screen. Common manifestations include a flickering display, headlights activating autonomously, or unresponsive buttons. While these issues may not directly impede driving, they indicate moisture in the auxiliary electrical system, which could lead to permanent damage if not addressed promptly.

Steps to take if your EV is water damaged

If an electric vehicle is suspected of water damage from flooding, owners must remember not to charge it, turn on the ignition, or attempt to restart it. The vehicle should be parked in a dry, well-ventilated area, away from direct sunlight, to allow for natural evaporation. Owners can carefully wipe clean the charging port and contact pins. However, the most effective approach is to transport the vehicle to an authorized service center for a thorough inspection by qualified technicians before any further use.

Ho Tan