Battery and motor for a speed bike: choosing the right capacity and motor

A speed pedelec (or speed bike ) is designed for fast, regular journeys—typically commuting—with assistance that can reach up to 45 km/h depending on the model and its homologation. But in real-world use, what makes the difference isn't just the "45 km/h on the spec sheet": it's the actual range , the quality of the assistance (acceleration, hill climbing), and the long-term reliability of the battery and motor.

This guide helps you choose the right battery (capacity, single vs dual) and the right motorization (central motor vs rear wheel), with simple guidelines and comparison tables.

1) Capacity and autonomy: 500–800 Wh… and beyond

Understanding “Wh” (the basic principle that avoids mistakes)

A battery's capacity is expressed in Wh (Watt-hours) . The more Wh, the more "reserve" you have to drive for a long time... under the same conditions .

But battery life varies enormously depending on:

• your weight + load (bag, lock, etc.)

• the elevation change (slopes)

• wind and temperature (cold reduces battery life)

• tire pressure

• the level of assistance (the higher the level, the more it consumes)

• your style (accelerations / steady speed)

Simple guidelines: what capacity for what use?

Here is a practical grid (to be adapted according to terrain + weather + level of assistance).

Key takeaway: if you want to maintain a comfortable range in winter, uphill, or with a high level of assistance, aim higher than your “on-paper” requirement.

2) Dual battery: for whom, and why?

The dual battery is not a gimmick: it's the simplest solution if you want to:

• making long journeys without recharging at the office

• drive fast and often (high assistance) without stressing

• to maintain autonomy even when it's cold

• carrying weight (bag, computer, equipment, etc.)

When it's really useful

You are a good candidate for a dual battery if:

• You travel 50 km/day or more (especially with hilly terrain)

• You drive all year round (winter included)

• You want to avoid daily recharging (or you don't have an accessible outlet)

Tip: Some people prefer a single "large" battery rather than a dual one. The important thing is your specific situation: distance, terrain, frequency, weather.

3) Engine: mid-drive vs. rear-wheel drive (torque, traction, feel)

The choice of engine has an impact:

• the sensation (natural vs “push”)

• the capacity on the slope

• efficiency (consumption)

• maintenance and long-term cost

Simple comparison: mid-drive vs. rear-wheel drive

In speed pedelecs , both are frequently encountered. The right choice depends mainly on your terrain:

• Many hills / frequent starts → advantage of a mid-engine

• Fast, mostly smooth journeys → very pleasant rear wheel

4) Torque (Nm) & “45 km/h”: what you really need to understand

The key point

The 45 km/h depends mainly on the category/homologation and the configuration of the system (assistance limit).
The couple (Nm) , on the other hand, focuses primarily on:

• acceleration (starting from a stoplight, resuming driving)

• the ability to maintain a high speed on an uphill section

• comfort when you are carrying a load or facing the wind

Practical guidelines (without getting lost)

• If you mainly ride in the city/flat areas , look for smooth assistance and a suitable battery: a “moderate” torque may be sufficient.

• If you have hills or want strong acceleration, choose a system known for its solid torque and intelligent assistance management.

A question to ask yourself: “Do I want to climb fast or climb easily ?”
If you want to climb quickly AND maintain comfort, you will need a more "powerful" system... and a battery to match.

5) Optimize battery life (without changing the battery)

Before paying more for a larger capacity, you can often gain 10–30% more battery life with simple habits:

Autonomy checklist (simple and effective)

• Tires : correct pressure = less rolling resistance

• Assistance : use an intermediate mode, and reserve the maximum for the hills.

• Cadence : spinning a little faster avoids "straining" the motor

• Weight : avoid unnecessary weight in the bag

• Temperature : Keep the battery away from the cold (if removable)

• Transmission : clean and lubricated chain = better efficiency

• Acceleration : "smooth" starts = fewer fuel consumption peaks

6) Charging, life cycle and best practices (battery + motor)

Battery: Best practices to extend lifespan

• Avoid leaving the battery at 100% or 0% for extended periods.

• If you are storing it for several weeks: store it partially loaded (and in a dry place).

• Allow the battery to return to temperature (especially in winter) before recharging.

For detailed maintenance recommendations (storage, charging, winter), you can follow the official Bosch advice here: battery care and maintenance

Engine: “smart” maintenance

• Gentle cleaning (no high-pressure jets on electrical areas)

• Regular checks of brakes/transmission (a speed bike goes fast: wear follows)

• Regular servicing is recommended if used intensively.

Concrete examples (at BatooBike): large capacity for longer rides

Even though not all bikes are speed pedelecs, looking at "long range" models helps to get an idea of ​​the capabilities that are interesting for regular use.

• The NCM Moscow Plus is a good example of a versatile bike with a high-capacity battery (practical if you are looking for comfortable range on a daily basis).

• The NCM Milano Plus also illustrates very well the “comfort + autonomy” combination, often sought after for regular and long journeys.

Points of concern regarding “speed pedelec” (Switzerland)

If you buy a high-speed e-bike (up to 45 km/h) , the requirements are different from those for a 25 km/h e-bike (license plate, equipment, etc.). The official summary is available here: OFROU/ASTRA – Specific rules for slow/high-speed e-bikes

FAQ – Battery & motor of a speed bike

What battery capacity do I need based on my usage?

If you do less than 25 km/day on flat terrain: 500–625 Wh may be sufficient.
For 25–50 km/day : aim for 625–800 Wh.

Beyond (terrain, cold, high assistance): 800–1000 Wh or dual battery .

How to optimize battery life?

Proper tire pressure, appropriate assistance mode, consistent cadence, limited weight, battery protected from the cold, clean drivetrain. These are the easiest gains.

Mid-drive or rear-wheel drive: which to choose?

• Central : ideal for coasts, natural feel, versatility.

• Rear wheel : very pleasant for fast commuting, "push" sensation, simple for everyday use.
  Choose according to your terrain (flat vs hilly) and your style (sport vs comfort).

What torque (Nm) is needed to reach 45 km/h?

The 45 km/h speed limit depends primarily on homologation and the assistance level. Torque is mainly used for strong acceleration and maintaining performance uphill . If you have hilly terrain, look for a system known for its torque and intelligent assistance management.

How to maintain the battery and engine?

Battery: avoid long storage at 100%/0%, store partially charged, dry, at moderate temperature.

Engine: no high-pressure jet, gentle cleaning, regular checks (brakes/transmission) and overhauls if used intensively.