Electric bike charging time: how to optimize your battery's charge

Recharging an electric bike is as easy as 1-2-3. But how long does it take, and why? How important is the type of charger, and how can you improve battery life? Here are our explanations and tips to find out.

The charging time of an electric bike is the time required to fully fill the battery with electricity. The time required for a full charge depends on two factors:

• Storage capacity in watt-hours (Wh) or ampere-hours (Ah)
• Load power in W (sometimes indicated in amperes or A).
  
  

As a reminder, if you've forgotten your college physics lessons: P = U x I or Power = Voltage x Intensity. Since most VAEs operate on 36 volts, multiply the current by 36 to calculate the power. Example for a power of 10 Ah: 36 x 10 = power of 360 Wh.

Virtually all electric-assist bicycle batteries on the market use lithium-ion (or Li-ion) technology, with cells often supplied by LG or Samsung. It is denser in energy, discharges less during storage, is less sensitive to extreme temperatures and performs better than older lithium-polymer (LiPo), lead-acid or nickel-metal-hydride (NiMh) acid batteries.

It takes around 7 hours to fully recharge a battery, but we'll see how different factors affect this time.

Each battery system has its own display, as there is no standard. However, the charge level can be read:

• On the bike's display,
• On a multi-light gauge on the bike,
• On a color-changing button,
• If you charge the battery off the bike, the battery may have its own gauge.
• On your bike application such as Bosch eBike.

If you don't have a display or indicator light, you'll have to consult the charger. Generally speaking, the charger indicator is red when charging, and green once the battery is fully charged.

The vast majority of battery capacities range from 250 to 750 Wh (or 7 to 20 Ah). It's not complicated: a 250 Wh battery (common on a road bike) will charge three times faster than a 750 Wh battery (more common on a electric cargo bike) with a charger of identical power.

Speaking of chargers, their power and current have a direct influence on charging time. A 4 amp charger - considered a fast charger - charges twice as fast as a 2 amp charger, or a 100 W charger takes half as long as a 50 W charger (at the same voltage). Here are some examples of recharging times for an electric bike battery:

• 10 Ah with 2 A charger: 5 h,
• 16 Ah with 4 A rapid charger: 4 h,
• 500 Wh with 100 W charger: 5 h.

Cold weather alters battery performance. Recharging is optimal above 10°C, so it will take longer if you charge in winter. Above 30°C, the outside temperature has no impact on charging speed, but can cause irreversible damage (failure, overheating, dead cells).

Battery manufacturers give lifetimes in cycles or years. It's more accurate to consider cycles, as endurance depends primarily on the number of recharges, and the nature of these recharges. One cycle determines a full or near-full charge. This means that if you charge a battery 10% of the time, you won't mathematically obtain 10 cycles.

The service life of an electric bicycle battery is a minimum of 500 charge cycles, and more generally 1,000 cycles according to Shimanosometimes more for the most enduring. If you recharge twice a week, or 100 times a year, your battery will last 10 years. In years, we estimate that a battery lasts 3 to 15 years, depending on use and the way it is charged.

If you're using a charger that comes with a battery, this is the most suitable, with 2 or 4 amps (2 or 4 A). With 4 amps, you can recharge twice as fast as with 2 amps.

Bosch PowerPack or Shimano Steps batteries, for example, accept both currents, while indicating a maximum current of 10 A. However, if you regularly charge beyond 4 A, your battery's lifespan is greatly reduced.

Unlike an electric car or scooter, an electrically-assisted bicycle does not require recharging while riding.

However, very few models use independent systems, such as the Zehus motor-battery (back-pedal recharging), or brake recharging systems like the Vefaa Bonjour Techno. However, this regeneration is very low compared to consumption, at best 10%.

Alongside lithium-ion batteries, another supercapacitor technology, like Pi-Pop, recharges the bike only during deceleration and braking.

Just as you would with your phone, laptop or electric car, a few simple tricks will extend the life of your EAB's battery:

• If you have a choice, load as slowly as possible,
• Charge the battery at least once a month,
• Store the battery at 80% for long periods of downtime, to avoid deep discharge,
• Do not charge or discharge to extremes (prefer 20-80%).
• At worst, don't leave your battery empty or 100% connected.

Frequent charging above 80%, and especially close to 90%, increases the number of cycles consumed and therefore reduces long-term capacity.

If you don't want to exceed a certain percentage, use the programmed charging function if you have one. It's available on your connected electric bike app, or directly on the charger.

Discharging a VAE battery to 0% is highly inadvisable, and should be reserved for emergencies only. This can permanently reduce your battery's capacity, especially if you repeat this regularly. Fortunately, manufacturers introduce a "buffer", an inaccessible capacity that acts as a safety device to prevent full discharge.

If a complete discharge occurs, the battery risks a "deep discharge", during which it becomes impossible to recharge. Only a professional can intervene at this stage, with no certainty of being able to save the battery.

If you study the battery stickers or read the user manual, you'll see that there are many precautions to take:

• Use the appropriate, certified charger,
• Avoid extreme temperatures (+50°C or -20°C),
• Do not recharge in direct sunlight,
• Do not load near liquids or water,
• Place the charger on a hard, heat-resistant surface,
• As a precaution, do not charge your battery in front of an exit door, in case of an incident.

The charging time of an electric bike battery no longer holds any secrets for you. You now know why and how to optimize charging time, in complete safety. There's nothing tricky about using a suitable charger, taking care to charge under the right conditions (ambient temperature, etc.), without going to extremes.

To find out more, read the user manual for your Bosch battery and follow the precautions given by bike manufacturers to avoid any risk.