1. Cycle Life Characteristics
Nickel-metal hydride batteries exhibit a cycle life exceeding 500 cycles under standard IEC testing protocols. This lifespan is influenced by:
Charge-discharge regimens (e.g., depth of discharge, current rates)
Ambient temperature: Optimal performance at 10℃–30℃; temperatures >35℃ accelerate degradation
Usage patterns: Shallow discharges (e.g., 20% depth) can extend cycles to 10,000+ in specific applications, though practical use typically achieves 500–1,000 cycles
In hybrid electric vehicles (HEVs), optimized management enables 8+ years of service with 2,000–5,000 cycles
2. Safety Characteristics
Ni-MH batteries feature inherent safety mechanisms due to material and structural design:
Reversible safety valve: Automatically releases gas when internal pressure exceeds thresholds (e.g., during overcharge/short-circuit), preventing explosions
Non-flammable electrolyte: Aqueous potassium hydroxide (KOH) eliminates fire risks, contrasting with lithium-ion chemistries
Abuse tolerance: Passes nail penetration, crush, and thermal tests without combustion
. Toyota’s 20+ million HEV batteries record zero thermal runaway incidents
3. Charging Characteristics
Key parameters govern efficient charging:
Voltage limits: Cut-off voltage typically set at 1.4V/cell; higher currents or low temperatures (<0℃) increase voltage
Temperature sensitivity:
Ideal range: 10℃–30℃ (charging efficiency >90%)
Critical thresholds: Charging prohibited below 0℃ or above 45℃
Fast-charging requirements: Currents >0.2C necessitate voltage/temperature monitoring to prevent damage
4. Discharge Characteristics
Discharge behavior depends on operational conditions:
Nominal voltage: Stable 1.2V platform under standard loads
Performance impacts:
Factor Effect
High current Voltage drop; max continuous discharge: 1C–3C (cell-dependent)
Low temperature Capacity reduction (e.g., 70% retention at -40°C)
Cut-off voltage: 0.9V–1.0V (per IEC); values <0.8V cause irreversible damage
5. Self-Discharge Characteristics
Self-discharge rates are temperature-dependent:
Room temperature (20℃): 10%–15% capacity loss/month
Elevated temperature (40℃): Losses exceed 20%–30%/month
This stems from hydrogen desorption in alloys and electrochemical side reactions
6. Long-Term Storage Characteristics
Ni-MH batteries demonstrate capacity recovery after prolonged storage:
Capacity decay: After 1 year, capacity may drop to 80%–90% of initial value
Recovery method: 3–5 shallow charge-discharge cycles restore original capacity
Optimal storage: Charge to 40%–60% state-of-charge (SOC) at 10℃–25℃ to minimize degradation
