1. Battery cell voltage difference is normal

An electric vehicle battery pack consists of many battery cells connected together. However, there will always be a difference in voltage between battery cells. Some possible causes include:

• Due to the production process: Each battery cell produced is not exactly the same. The processes of manufacturing and making cell contacts cannot avoid small differences in capacity, internal resistance, and especially voltage. Even within the same production line, differences still appear.

• Conditions of use and environment: Because of these differences in the manufacturing process, battery cells will have slight variations from each other during use. The longer the battery is used with greater capacity under different temperature conditions, the voltage difference between the cells will be caused.

To solve the problem of battery cells always having voltage differences, new battery management systems (Battery Management System - BMS) were born. BMS helps monitor and adjust the voltage of each cell to ensure balance of the entire battery pack. Ensuring this uniformity helps you maximize the performance of the entire battery pack. Note that, even with the help of a BMS, ensuring that the battery cells do not deviate in voltage, especially in a short time, is still impossible. However, with the presence of BMS, you can rest assured that in the long run, the BMS will work continuously to balance the battery cells in your battery pack.

In addition, BMS also has other functions for protection. For example, over-current, over-temperature, over-voltage protection, etc. These functions are important for a battery system because it ensures safety and helps ensure battery life. But these features are not directly related to the voltage difference of the battery cells.

2. How Dat Bike's BMS determines battery full threshold

Imagine each battery cell as a glass of water, a battery pack is many glasses of water connected in series. Charging the battery to 100% is using a faucet and filling up water glasses at the same time.

However, as mentioned in part 1, battery cells will have a certain pressure difference during use (charging/discharging). In the case of glasses of water, there will also be glasses containing less water and glasses with more water.

Here we will talk a little more about the operating voltage range of LFP cells on Quantum. Battery cells operate in the voltage range from 2.7V to 3.65V. Therefore, 3.65V is the fully charged battery cell level. If a battery cell reaches 3.65V, the BMS thinks the vehicle is fully charged and disconnects the power to ensure the safety of the battery cell. In the example of a glass of water, 3.65V is the water level when filling the glass.

If you use a faucet to fill all the glasses at the same time, with the condition of cutting off the water when one glass is full, a phenomenon will occur: some glasses will be filled with water first (because there is already water in them) and the faucet will stop pumping. , while some glasses are not yet full (the glasses originally had less water or no water).

The image illustrates charging battery cells as well as filling water glasses

The fact that a battery cell is full of voltage, or a glass of water is filled is a signal for the BMS to say "enough" and the charger will stop supplying power to the battery. However, in reality, there will be some battery cells that only reach 95, 96%, depending on the pressure difference. This explains why some cars cannot be charged to 100% when first purchased.

3. How Dat Bike's BMS determines the battery drain threshold

Another phenomenon affected by the voltage difference of battery cells is the fact that some vehicles have a battery percentage > 0 but the vehicle suddenly turns off.

As mentioned in part 2 , the battery cells on Quantum operate in the voltage range from 2.7V to 3.65V. When charging, 3.65V is the basis for the BMS to stop charging. During the discharge phase when driving, if any battery cell reaches 2.7V, the BMS will signal "battery empty" and the vehicle will stop operating.

Once again, we need to reiterate that battery cells always have voltage fluctuations for many objective reasons. So when one battery cell reaches 2.7V, there are still many other battery cells that still have electricity (similarly when draining all water glasses, the glass with the least amount of water will run out first). This explains the fact that some cars have a battery percentage > 0% but suddenly turn off the car.

4. Change the way Dat Bike's battery percentage is calculated and instructions for charging the Quantum bike properly

At this point, you understand why some cars cannot charge to 100%, or cars with a battery percentage > 0 turn off by themselves. The voltage deviation of the battery cells can be overcome by maintaining a full charge at least once a week when you first buy the car. Over time, this will help improve the voltage deviation of the cells, helping the battery pack operate stably and achieve more accurate performance.

In the recent Firmware v1.3.2, Dat Bike has changed the way to calculate the battery percentage so that customers can actively monitor the balancing process of battery cells day by day, as well as help newly purchased vehicles reach the status quo soon. Stable performance as announced by Dat Bike.

To better understand this change, let's consider the case where there is a large difference between cells and you cannot use 100% of the battery pack's capacity. Let's say in this case you can only use 85% of the capacity. According to the old calculation method, when the BMS stops charging, the vehicle will automatically determine that it is 100% charged. This will cause the vehicle to lose power when the display reaches 15% (actually the battery is exhausted).

According to the new calculation, instead of determining the 100% milestone when the battery is full, the car will determine the 0% milestone when the battery is depleted (BMS stops discharging). This means you will only get a charge up to 85%. So, in this case, instead of the LCD displaying 100% to 15% (when the battery is depleted), the LCD will display from 85% to 0%. Gradually, over time of use, the BMS will balance the battery, then you will be able to charge it to 100% and you can use the full performance of your battery pack.
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This will fix the problem that the battery percentage is not as accurate as before (for example, the number displayed is 100% but in reality the car only has a lower percentage charge, so it will easily lose power when it is almost exhausted).

However, changing this new way of calculating battery percentage will cause some cars, after updating Firmware v1.3.2 , to no longer be able to charge the battery to 100%. Please rest assured to monitor your battery percentage and improve it by:

1. If the vehicle cannot be charged to 100% but the charger has been disconnected, switch the LCD screen to the technical screen (Hold the left brake + press and hold passing for 1s, then quickly press passing twice) unplug the charger (let the BMS balance the cell) and monitor the max parameter when it falls around 3.39, then plug in the charger again.
2. You should charge your car's battery once a day until the battery cells are balanced with each other, which is equivalent to charging the battery to 100% per charge. In addition, Dat Bike also recommends that users fully charge the bike overnight at least once a week to ensure voltage balance between battery cells.

These actions help balance the capacity between battery cells better, making more optimal use of the battery's capacity. You can monitor the improvement yourself by gradually increasing the car's charge to 100%.

Conclude:

Through the above article, here is the main information you need to know:

1. It is normal for battery cells on newly purchased electric vehicles to have voltage differences. This can be overcome by regularly charging the battery, especially in the early stages of buying a car. In addition, Dat Bike also recommends that users fully charge the bike overnight at least once a week to ensure voltage balance between battery cells.
2. The problem of not being able to charge the car to 100% is due to the fact that newly purchased cars have battery cells with voltage deviations and due to changes in the algorithm for calculating the car's battery percentage. You can gradually fix it by unplugging the charger and plugging it back in. Maintaining charging once a day will help the car soon reach a state of battery balance, and users can see this by noticing the maximum percentage of charged battery that will gradually increase over time.
3. Quantum vehicles updated to Firmware v1.3.2 or later will fix the phenomenon of battery >0% but the vehicle stops working suddenly. Instead, the car will signal that the charge is not fully charged by displaying a percentage < 100%. Everyone can rest assured to improve by following the instructions given by Dat Bike above.