The battery is the “heart” of an electric bicycle. Over time, its performance naturally degrades. If you don’t monitor it, you may experience:
Reduced range
Weak acceleration
Overheating
Premature battery failure
This guide explains how to scientifically assess your e-bike battery’s health, focusing on three key indicators: voltage, internal resistance, and capacity fading.
Battery voltage directly reflects its health. The typical e-bike voltages are 36V, 48V, 52V, or 60V.
Measure the voltage when the battery is not connected to the motor.
Normal: Slightly below nominal voltage (0.1–0.3V).
Warning signs:
Voltage drops quickly after full charge (>0.5–1V)
Voltage below 80% of nominal → check or replace
Measure during riding or discharging.
Rapid voltage drops indicate high internal resistance and aging.
Example: A 48V battery dropping below 40V under load → significantly reduced range.
Internal resistance (measured in milliohms, mΩ) reflects battery chemistry and structure.
New battery: ~20–50 mΩ (varies by capacity & type)
Aging battery: Internal resistance increases → efficiency drops, heating increases
Symptoms of high internal resistance:
Noticeable heating during charging
Rapid voltage drop under load
Reduced motor performance
Tools: Digital battery internal resistance tester or smart BMS.
Capacity fading shows how much usable energy the battery can store:
New battery: 100% capacity
Replacement threshold:
Below 70–80% → recommend replacement
Below 50% → severely affects range & performance
Measurement Methods:
Real-world range test:
Fully charge, ride a fixed distance, compare actual range to rated range.
Professional discharge test:
Use an electronic load to measure full discharge capacity (Ah) against nominal capacity.
| Indicator | Normal | Warning / Needs Attention | Recommendation |
|---|---|---|---|
| Static Voltage | Close to nominal | Drops quickly; <80% of nominal | Inspect or replace |
| Load Voltage | Stable | Rapid voltage drop under load; weak acceleration | Replace |
| Internal Resistance | 20–50 mΩ | >2× original, noticeable heat | Replace |
| Capacity Fading | 90–100% | <70% | Replace |
Regular checks: Every 6–12 months, measure voltage and internal resistance
Consider environment: High temperature, humidity, and fast charging accelerate aging
Choose high-quality cells: Reliable brands degrade slower
Monitor BMS: Overcurrent, overcharge, and temperature protections extend battery life
To determine if an e-bike battery needs replacement, focus on:
Voltage – rapid drops indicate aging
Internal resistance – high resistance means low efficiency and overheating
Capacity fading – capacity below 70% → time to replace
Replacing an aging battery promptly ensures safe riding, reliable power, and stable range, while also protecting the motor and controller.
The battery is the “heart” of an electric bicycle. Over time, its performance naturally degrades. If you don’t monitor it, you may experience:
Reduced range
Weak acceleration
Overheating
Premature battery failure
This guide explains how to scientifically assess your e-bike battery’s health, focusing on three key indicators: voltage, internal resistance, and capacity fading.
Battery voltage directly reflects its health. The typical e-bike voltages are 36V, 48V, 52V, or 60V.
Measure the voltage when the battery is not connected to the motor.
Normal: Slightly below nominal voltage (0.1–0.3V).
Warning signs:
Voltage drops quickly after full charge (>0.5–1V)
Voltage below 80% of nominal → check or replace
Measure during riding or discharging.
Rapid voltage drops indicate high internal resistance and aging.
Example: A 48V battery dropping below 40V under load → significantly reduced range.
Internal resistance (measured in milliohms, mΩ) reflects battery chemistry and structure.
New battery: ~20–50 mΩ (varies by capacity & type)
Aging battery: Internal resistance increases → efficiency drops, heating increases
Symptoms of high internal resistance:
Noticeable heating during charging
Rapid voltage drop under load
Reduced motor performance
Tools: Digital battery internal resistance tester or smart BMS.
Capacity fading shows how much usable energy the battery can store:
New battery: 100% capacity
Replacement threshold:
Below 70–80% → recommend replacement
Below 50% → severely affects range & performance
Measurement Methods:
Real-world range test:
Fully charge, ride a fixed distance, compare actual range to rated range.
Professional discharge test:
Use an electronic load to measure full discharge capacity (Ah) against nominal capacity.
| Indicator | Normal | Warning / Needs Attention | Recommendation |
|---|---|---|---|
| Static Voltage | Close to nominal | Drops quickly; <80% of nominal | Inspect or replace |
| Load Voltage | Stable | Rapid voltage drop under load; weak acceleration | Replace |
| Internal Resistance | 20–50 mΩ | >2× original, noticeable heat | Replace |
| Capacity Fading | 90–100% | <70% | Replace |
Regular checks: Every 6–12 months, measure voltage and internal resistance
Consider environment: High temperature, humidity, and fast charging accelerate aging
Choose high-quality cells: Reliable brands degrade slower
Monitor BMS: Overcurrent, overcharge, and temperature protections extend battery life
To determine if an e-bike battery needs replacement, focus on:
Voltage – rapid drops indicate aging
Internal resistance – high resistance means low efficiency and overheating
Capacity fading – capacity below 70% → time to replace
Replacing an aging battery promptly ensures safe riding, reliable power, and stable range, while also protecting the motor and controller.