Even though LiFePO4 batteries are very thermally stable (with a thermal runaway trigger temperature of 486℃), the BMS (Battery Management System) is still the essential warranty for performance and safety. For instance, taking a 100Ah battery pack, the BMS, whose sampling precision is voltage ±5mV, maintains single cell voltage drift within 3.2V±0.05V (the drift amounts to ±0.3V when without a BMS), avoiding induced accelerated capacity aging from overcharging (>3.65V) or overdischarging (<2.5V) (loss of capacity is 0.8% when doing one overcharge and 3% when without a BMS). The UL 1973 test certification shows thermal runaway potential of LiFePO4 battery packs with BMS has dropped from 0.12% to 0.0037%, and thermal spread time has been increased to > 30 minutes (only 5 minutes without BMS).
Temperature regulation relies on BMS: its 0.1℃ resolution sensor can adjust the temperature difference of battery cells within ±2℃ (±8℃ during natural cooling mode), reducing the standard deviation of cycle life from ±15% to ±3%. During the high-temperature test at 45℃, the active cooling initiated by BMS (≤5W power consumption) reduced the capacity attenuation rate to 0.01%/cycle (0.05%/cycle without temperature control). Results of a 1MWh energy storage operation in Norway reveal that the balancing process of the BMS has increased the capacity dispersion of the battery pack from the initial 3.2% to merely 5.7% after 2,000 cycles (18% without balancing), and the available energy over the lifetime has been increased by 23%.
The cycle life has been significantly improved. The LiFePO4 battery with BMS achieved 4,000 cycles at 80% DoD (capacity retention rate ≥80%), while the control group without BMS dropped its capacity to 70% after 1,500 cycles. The real experiment of Tesla Powerwall shows that the charging algorithm of BMS has improved the charging efficiency from 88% to 95% (lengthened the peak power maintenance time by 27%), and SOC estimation error is ≤±1% (±8% without BMS). Avoid lithium precipitation caused by deep discharge (probability of lithium precipitation reduced from 0.15% to 0.002%).
In cost-effectiveness, the cost of BMS is 8% to 12% of the total cost of the battery pack but can reduce the entire life cycle cost. A European RV user example indicates that the lifepo4 pack (12V 200Ah) with BMS has a maintenance cost of just €15 in 5 years (€120 for the pack without BMS), and because of over-discharge protection, the frequency of battery replacement is lowered (the replacement cycle is increased from 3 years to 10 years), and the return on investment is boosted by 41%. BYD Blade Battery’s BMS, featuring double closed-loop control of temperature and voltage, has reduced the battery pack failure rate from 0.5 times per thousand cycles to 0.03 times per thousand cycles, lowering insurance costs by 62%.
The need for safety case verification: In a recent fire accident in one of California’s energy storage power plants in 2023, it was discovered that an uncontrolled LiFePO4 battery pack triggered a thermal runaway chain reaction as a result of a single-cell voltage imbalance (with a worst-case shift of 0.8V), while the adjacent battery pack having a BMS successfully isolated the fault and reduced the loss by $2.3M. IEC 62619 standard requires energy storage LiFePO4 batteries to be developed with a BMS, the overcurrent protection response time of which is ≤50ms (> 500ms without a BMS), and short-circuit current cut-off efficiency is 99.99%. During the needle-puncture test, the surface temperature at the top of the battery with BMS was only 68℃ (152℃ without BMS), and there was no open flame or explosion.
Regulatory and certification requirements: UN38.3 certification requires export LiFePO4 battery packs to be integrated with a BMS to apply three-level protection of overcharge, overdischarge, and short circuiting. In accordance with German TUV’s report, through the active balancing method of BMS, the capacity consistency of battery packs is ensured at ±6% after retirement (±25% without BMS), and the value of secondary use is increased by 37%. As per Chinese GB/T 36276 regulation, the BMS SOC estimation accuracy should be ≤±3% or otherwise it will be disqualified from obtaining the new energy subsidy (￥200 per kWh subsidy). Norwegian Maritime Authority requires the Marine LiFePO4 battery’s BMS should have IP67 waterproof and 5G vibration protection to ensure failure rate should not exceed 0.001 times per year under severe environments.