Answer: The runtime depends on the battery's energy capacity (Wh) and motor load (W), with significant discrepancies between theoretical and actual values.
Core Formulas and Definitions
Battery Energy (Wh) = Voltage (V) × Ampere-Hour (Ah)
Load Power (W) = Power required for stable motor or system operation
Theoretical Run Time (hours) = Battery Energy ÷ Load Power
Example: A 432 Wh battery powering a 350 W motor yields a theoretical runtime = 432 ÷ 350 ≈ 1.23 hours (approx. 74 minutes).
However, this represents an idealized estimate. Actual operation must account for various losses and influencing factors.
Real-World Factors and Degradation Correction
The following factors significantly impact actual runtime:
1. Load Fluctuations and Peak Power: Frequent high-power operation or acceleration of the motor subjects the battery to high load conditions, directly reducing runtime.
2. Conversion and Internal Resistance Losses: Energy inevitably suffers losses during transmission and conversion. These losses occur within the battery itself, the electronic control unit (ECU), wiring, and various interfaces, thereby reducing overall efficiency and effective range.
3. Deep Discharge Prevention Strategies: To extend battery lifespan, systems typically prevent batteries from discharging completely to 0%. For example, many devices limit usable capacity to around 80%, meaning even if the battery has a rated capacity, its actual usable power is consequently reduced.
4. Temperature: Ambient temperature significantly impacts battery performance. In cold conditions, the battery's chemical activity decreases, leading to reduced performance; conversely, high temperatures accelerate internal degradation processes, similarly shortening range.
5. Battery Degradation: As the number of charge-discharge cycles increases, the battery's chemical properties gradually deteriorate, causing its maximum capacity to slowly decrease. This is the fundamental reason why battery life diminishes over time.
Example: For a 432 Wh battery limited to 80% discharge with 10% efficiency loss, usable energy is 432 × 0.8 × 0.9 = 311 Wh. Powering a 350 W system yields an endurance of 311 ÷ 350 ≈ 0.89 hours (approx. 53 minutes).
Application Scenario Estimates45
Light load or cruising mode (average motor power 150–250 W): A 432 Wh battery may support 2–3 hours of runtime
Flat terrain + moderate pedal assistance: 15–70 miles (24–112 km) range achievable, depending on battery capacity, assistance level, riding mode, and terrain
Heavy load or frequent climbing: Range may drop to 30%–60% of theoretical values
How to Select Batteries for Target Range Requirements
1. Determine average power demand (W)
2. Set target ride duration (hours)
3. Account for capacity redundancy and discharge strategy (e.g., use 70–85% available capacity)
4. Required battery capacity = (Power × Time) ÷ Usable ratio
Example: For a system with 300 W average power, 2-hour target duration, and a 0.8 usable ratio:
Requirement = (300 × 2) ÷ 0.8 = 750 Wh battery capacity.
