Don't buy MKEPA e-bike batteries
Why do e-bike batteries explode?
In 2023, I bought a battery pack from MKEPA at AliExpress. This battery is actually a dangerous bomb because it is poorly manufactured.
In this article, I will use this battery as example to describe why lithium batteries explode so often and get fire.
A thin plastic film of 0.1mm is the borderline between life and death
To ensure safety, it is essential to continuously monitor the battery and immediately disconnect it if it becomes overloaded.
The individual battery cells must also be reliably insulated from each other to prevent short circuits. This definitively will lead to spontaneous combustion. However, in many battery packs, such as the MKEPA, the insulation consists of only a 0.1mm thin plastic foil that typically surrounds the cells. This foil is not suitable for this purpose, and it is a major factor behind numerous e-bike battery fires. The thin plastic film will degrade over time and will easliy cause short circuits due to vibrations during driving.
The same applies to the busbar insulation, which is also not safe, as depicted in the image:
Bad battery management systems causes e-bike battery fires
The Battery Management System (BMS) is a crucial safety component in lithium-ion batteries. However, the BMS in this MKEPA battery is severely lacking in safety features. It lacks overload protection, temperature monitoring, and cell balancing, all of which are essential for safe battery operation. I tested the overload protection: this caused the short-circuiting of two power MOSFETs. Of course, the BMS was not able to protect the battery anymore.
The BMS is extreme simple and contains just 10 DW01A chips connected in series, as illustrated in the circuit diagram:
False MKEPA capacity claims
Not only is the MKEPA battery dangerous, its capacity is just 1/5 of the specified capacity:
The battery's actual capacity is only 4050mAh, which is far lower than the advertised 20,000mAh. This indicates that the seller has provided misleading information. I have measured the capacity with my Bluetooth Watt meter dongle, this is equipped with a precise LTC2944 fuel gauge chip.
First, I fully charged the battery to 42V. Then, I discharged it through a 13Ω resistor, while the current, voltage, and capacity were measured. The results clearly show a capacity of just 4050mAh:
This MKEPA battery can never have capacity of 20,000mAh. That would require that the 18650 cells have a capacity of 5000mAh, but cells of this capacity are not invented yet in 2023. Instead, the used 18650 cells have an unusually low capacity of just 1Ah each.