Fast charger for electric scooters: the real time savings and its limitations
A fast charger can reduce the charging time of a large scooter battery from a whole night to around an hour. However, it cannot be connected to just any battery: the cells, the BMS (Battery Management System), the connector, and the charging cables must be able to handle the current, and the charger must be precisely calibrated to the battery pack's voltage. When used correctly, it's a fantastic tool for enabling back-to-back rides or track sessions; when used improperly, it can damage the battery and potentially put it at risk.
The essentials
- The charging time is calculated by dividing the amount of energy to be replenished (in Wh) by the charger's power (in W), plus a margin to account for the end of the charging process.
- The battery must be designed for fast charging: this includes the cells, the Battery Management System (BMS), the charging connector, and the charging wiring.
- The charger must have the correct final voltage, adjusted for the number of cells in series.
- Fast charging generates more heat in the battery cells. Therefore, it should be reserved for situations where it's truly needed, and regular, slower charging should be used more often.
- A charger with several kilowatts requires appropriate electrical installation.
Time savings, backed by data
The calculation is simple: energy to be replenished divided by the charging power. A 2,880 Wh battery (72 V, 40 Ah) charged by a charger of a few hundred watts takes several hours, often a whole night. Our UltraCharge "GTK" 4,000 W charger can recharge a 2 to 3 kWh battery in about an hour.
The final part of the charging process is always slower: as the battery approaches full charge, the charger maintains the voltage, and the current gradually decreases. This phase exists with all chargers; fast charging primarily benefits the initial part of the process, which represents the majority of the energy transfer. The calculation method is detailed in our guide Wh, Ah, volts: calculating battery capacity.
What the battery needs to withstand
The cells
Each lithium battery cell has a maximum charging current specified by its manufacturer, which is often much lower than its discharge current. The charging current from the charger is distributed among the cells connected in parallel: a battery with many cells in parallel can accept a higher total current. This is often expressed in "C": charging at 1C means charging with a current equal to the battery's capacity, which theoretically takes about one hour. Power cells generally handle fast charging better than energy cells.
The Battery Management System (BMS) and the charging connector
Many Battery Management Systems (BMS) have a charging input with a limited current, which is much lower than the discharge current. The original charging connector, often small, is not designed for tens of amps; it would overheat. A battery compatible with fast charging has a BMS and connectors sized accordingly. This is the case with our Performance batteries, for example, the Performance 72V 40Ah battery for Dualtron Thunder and Thunder 2, which is advertised as compatible with super chargers.
Final voltage
The charger must stop charging precisely at the battery's full charge voltage: 84V for 20 cells in series, and 92.4V for 22 cells. An incorrect setting will overcharge all the cells. That's why we adjust the end-of-charge voltage and current of the UltraCharger before shipping, based on the voltage and connector of the battery pack specified in the order.
What fast charging costs the battery
The stronger the charging current, the more the cells heat up, and heat is the primary factor in the degradation of a lithium battery. Occasional fast charging, on a battery designed for it, is not a problem. However, repeatedly fast charging a battery that is already warm after a ride will accelerate its aging process.
There's also the issue of balancing: the BMS primarily balances the cells towards the end of the charging cycle, and does so slowly. A battery that is always charged quickly and disconnected as soon as the green light appears will not balance properly. Perform a full, slow charge regularly. The mechanism is explained in our guide on BMS and cell balancing.
Usage Precautions:
- Allow the battery to cool down after a ride before starting a fast charge.
- Never charge a cold battery: When the temperature is below 0°C, charging can cause metallic lithium to deposit within the battery cells, and the risk increases with the charging current.
- Charge the device on a non-flammable surface, in a well-ventilated area, and remain nearby during the charging process. Disconnect the charger when finished.
- Monitor the charging connector's temperature: if it gets hot, stop using it.
- Please check your power supply: a standard household outlet is designed for 16 amps, which is approximately 3.7 kW at 230V. A charger with several kilowatts draws a significant amount of power from the mains. Please ask us about the required power supply and have your electrical installation checked by a qualified electrician.
General best practices are outlined in our guide on how to charge your electric scooter battery.
| Usage: | Slow charging | Fast charging |
|---|---|---|
| Daily commutes | Ideal | Not very useful |
| Long ride with a break | Too slow | Useful, compatible with certain battery types |
| Track day | Too slow between sessions | The actual use case |
| Cell balancing | Regularly required | Do not replace it |
Workshop tip
Before purchasing a fast charger, make sure your battery supports it: an original battery with a small charging connector is almost never designed for fast charging. If you're aiming for fast charging, consider it when choosing your battery, with our electric scooter batteries that are compatible.
Frequently Asked Questions
Can I use a fast charger with my original battery?Generally, no: its Battery Management System (BMS) and charging connector are not designed for high currents. The connector would overheat, or the BMS would interrupt the charging process.
Does fast charging damage the battery?It puts more strain on the battery, especially due to heat. When using a battery designed for this purpose, used occasionally, and with cells at ambient temperature, the effect remains moderate. However, with regular use, the wear and tear is accelerated.
Why is the charging process slower at the end?When the battery is nearly full, the charger maintains the final voltage while the current gradually decreases to avoid exceeding the maximum voltage of the cells. This phase is present with all chargers.
Does the fast charger plug into a standard outlet?It depends on its power and your installation. Beyond a few kilowatts, you're approaching the limits of a standard household outlet. Have your electrical installation checked and contact us to find out what you need to consider.