Several lithium batteries can be connected in series to form a home battery pack, which can either power a variety of loads or be charged normally with a matched charger. Lithium batteries do not require any battery management system (BMS) to discharge. So why do all lithium batteries on the market have a BMS added to them?
The answer is: safety and longevity
Battery Mangement System (BMS) is used to monitor and control the charging and discharging of rechargeable batteries. The most important function of a Battery Mangement System BMS is to ensure that the battery stays within safe operating limits and to take immediate action if any individual cell begins to exceed those limits. If the BMS monitors the band voltage to be too low, it will disconnect the load and if the voltage is too high, it will disconnect the charger. It will also check the voltage or low voltage of each cell in the pack - which is often the cause of the lithium battery fires we see in the news. It can even monitor the temperature of the cells and disconnect the battery pack before it gets so hot that it catches fire. So, the Battery Management System BMS is what keeps the battery protected, rather than relying purely on a good charger or proper user operation.
Why don't lead-acid batteries (AGM, Doubtful Gel, Deep Cycle, etc.) need a battery management system?
Lead-acid batteries have a less flammable composition and they are much less likely to catch fire if there is a problem with charging or discharging. When the main cause has to do with the behavior of the battery when it is full. Lead-acid batteries are also made up of cells connected in series; if one cell is charged slightly more than the others, before the other cells are fully charged, it will only allow current to pass through while maintaining a reasonable voltage for itself, waiting for the other cells to catch up, and in this way the lead-acid batteries will "self-balance" as they are charged.
Lithium batteries are different. Rechargeable lithium batteries are mostly positive for lithium-ion materials, its working principle dictates that, in the process of charging and discharging, lithium electrons will run again and again on both sides of the positive and negative poles. If the voltage of a single cell is allowed to be higher than 4.25V (except for high-voltage lithium batteries), the anode microporous structure may collapse. The hard crystalline material may grow and cause a short circuit, and then the temperature will rise rapidly, eventually leading to a fire. When a lithium cell is fully charged, the voltage will rise suddenly and reach a dangerous level very quickly. If one cell in a battery pack has a higher voltage than the others, this cell will be the first to reach the dangerous voltage during the charging process, while the overall voltage of the battery pack has not yet reached the full value, and the charger will not stop charging. Therefore, the cell that reaches the dangerous voltage first will cause a safety risk. Therefore, controlling and monitoring the total voltage of the battery pack is not sufficient for lithium-based chemistries; the BMS must check the voltage of each individual cell that makes up the pack.
In a narrow sense, a battery management system BMS is used for the protection of large battery packs, typically lithium iron phosphate power cells with overcharge, overdischarge. Overcurrent, short circuit, cell balancing and other protection functions, some batteries may also need communication ports and data input and output and other display functions, such as Ruiding professional customized BMS.
Broadly speaking, Protection Circuit Board PCB (Protection Circuit Board), sometimes called PCM (Protection Circuit Module), belongs to the simple battery management system BMS, which is usually used for small battery packs. Typically used for digital batteries. Most of the time, it is used for 3.7V or 7.4V battery packs, it has four basic functions: overcharge, overdischarge, overcurrent and short circuit. Some batteries may also need PTC and NTC.
Therefore, to ensure the safety and long service life of lithium battery packs, a quality and reliable battery management system BMS is really needed.
