The high-voltage battery is one of the most critical and expensive components of an electric vehicle. Its condition directly impacts the vehicle's most important characteristics, including the ability to move at all. Manufacturers put in a lot of effort to protect HVB from external and internal factors, but car owners still face problems. As the number of electric and hybrid vehicles increases, services like battery repair and restoration are becoming more and more popular.

Structure of Electric Vehicle Batteries

Electric vehicle batteries consist of small cells with a voltage of 1.2 or 3.7V, depending on the type. Since the required output power is several tens of kW and the voltage can reach up to 800V, a large number of power sources are needed. These are assembled into modules (cells) of several pieces (usually from 4 to 12). Both the standard Battery Management System (BMS) and battery recovery equipment work with modules in nickel batteries and with individual cells in lithium batteries.

Cars use different types of batteries, with the most common being:● Nickel-metal hydride (Ni-MH)● Lithium-ion (Li-ion)
The first type is considered outdated and was mainly used in hybrids. However, today, even hybrids (like the Toyota Prius Prime hybrid battery) use lithium. Each type has its pros and cons. Ni-MH batteries are less efficient, almost unusable when charged below 20%, and difficult to charge over 80%. They are more prone to self-discharge. However, Ni-MH is relatively safe – it can only explode without catching fire.

Li-ion batteries significantly outperform Ni-MH in terms of parameters. They last longer, self-discharge is almost non-existent, and there is no memory effect (i.e., they can be charged from any point). Lithium batteries have a higher energy density. The main significant drawback is the exceptional fire hazard of lithium. When it is ignited, it is very difficult to extinguish. However, lithium can be controlled by the BMS (Battery Management System), a battery control system equipped in all electric vehicles with this type of battery.

And although the parameters of the two types of batteries differ, the main problems are roughly the same.

Main Battery Problems

The degradation of any battery is an inevitable process dictated by the laws of physics. Even with proper use of an electric vehicle, it averages about 2% of capacity per year. Since a battery is considered unusable when about 30% of its capacity is lost, this guarantees about 10-15 years of operation. However, there are factors that can significantly accelerate degradation.
OverheatingThe danger of overheating a high-voltage battery lies not only in the possibility of fire or explosion – this happens quite rarely. Excessive temperature is also stressful for the cells, leading to premature loss of capacity. In addition to general overheating, there is also local overheating when, in an unbalanced battery, the more charged cells bear more load, and the voltage of the hybrid vehicle or electric car battery drops.Balancing is required, but the car's BMS can only equalize the cells if they are in very good condition, with a small difference between them. And while Ni-MH batteries allow a voltage variance of 1.5V, in lithium batteries, the maximum is 50mV. The BMS often fails to balance the battery in time.Nickel batteries are more tolerant of overheating; for balanced operation, they just need to be charged to 100%. But the standard electronics will shut off at 80% for safety reasons. A special technique is needed: a trickle charge. This is already a kind of hybrid battery restoration, which is only possible with the use of special equipment.
Physical DamageElectric vehicle batteries are most typically located under the car's floor. This improves balance and handling but increases the risk of damage. Situations where HVB may suffer vary:
● Accidents● Hitting obstacles● Damage by forklift forks during sea transportation (relevant for cars from the USA)
Operating a vehicle with a damaged battery is dangerous. Mandatory inspection with a lithium or Ni-MH battery tester is required.In hybrid cars, batteries are often located under the rear seat, so air intakes are installed in the cabin. Through them, moisture (e.g., condensation or melted snow) can get into the battery, leading to contact corrosion and HVB imbalance. In general, moisture ingress inside the HVB is a very serious problem. In this case, a Li-Ion tester is also necessary.
Battery Chemistry ProblemsElectric vehicles vary in quality, as do their batteries. For example, Tesla batteries rarely fail, while Chinese HVBs are often not of the best quality. This is manifested in the fact that after a certain time – approximately six months – some modules begin to accept charge worse, which also leads to imbalance and battery failure. To determine which ones need to be balanced in time, a Li-Ion battery capacity tester is again necessary.

How to Deal with Battery Problems

High-voltage batteries do not fail completely and immediately. Mostly, issues initially arise in individual modules, which the electric vehicle's electronics cannot handle on their own. If not addressed, local issues can escalate into major ones. The owner has to find ways to restore the hybrid battery or replace the HVB cells in the electric car.

To monitor battery condition, diagnose, and repair at all stages, including:
● Capacity determination● Preparing HVB for installation in the car● Preparing for storage
We have released the MS800 diagnostic tester. This unique device allows solving many problems with Ni-MH and Li-ion batteries, preventing their malfunction and premature failure.