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Choosing the Best Batteries for an Electric Bike: Pros and Cons

/ 5 min read

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Good afternoon. I’ve decided to move my technical hobbies and projects to a separate platform to keep my main site focused. As you can see from the category, I’m currently planning an electric bike build. For now, it’s mostly theoretical, as the budget for a high-quality build is significant, and my current priority is my mortgage. However, I’m optimistic about making it happen.

This article serves as a personal reference and a systematized guide for anyone else looking into electric bike power sources. I won’t cover every battery type in existence—only those practical for e-bike builds. I’ll likely update this post as I learn more.

Lead-Acid Batteries

Invented in the mid-19th century, lead-acid batteries remain in use today with relatively minor changes. Most people recognize them from their use in cars and motorcycles.

Technical Characteristics:

  • Specific Energy (Wh/kg): 30–60
  • Theoretical Specific Energy Density (Wh/dm³): 1250
  • EMF (Charged): 2.11–2.17 V per cell (standard 6V or 12V configurations)
  • Cut-off Voltage (Discharged): 1.75–1.8 V per cell
  • Operating Temperature: -40°C to +40°C
  • Efficiency: ~80–90%

For electric vehicles, two specific types of lead-acid technology are common: AGM and GEL.

AGM (Absorbent Glass Mat) is the most affordable option in this class. It uses fiberglass mats between lead plates to bind the electrolyte. This allows the battery to be used in various orientations (e.g., on its side). Life expectancy is typically 200–800 cycles.

GEL batteries use a silica gel to immobilize the electrolyte. This design holds the plates firmly in place, reducing the risk of plate shedding or buckling. They are more robust and offer a longer life cycle of 350–1200 cycles.

Pros of AGM and GEL:

  • Very low cost compared to lithium.
  • Safer than Li-Ion/Li-Pol; physical damage won’t cause fires.
  • High vibration resistance.
  • GEL offers a respectable life cycle for the price.

Cons:

  • Extremely heavy.
  • AGM batteries have a short life cycle.
  • Lead oxide is toxic and environmentally hazardous.
  • Sensitive to overcharging.
  • Cannot be stored in a discharged state.

Nickel-Based Batteries (NiCd, NiMh)

NiCd (Nickel-Cadmium) batteries are often found in older power tools because they can handle high discharge currents and wide temperature ranges. However, their use is declining due to the toxicity of cadmium.

Technical Characteristics:

  • Specific Energy: 30–50 Wh/kg
  • EMF: 1.37 V
  • Operating Voltage: 1.35–1.0 V
  • Service Life: 100–900 cycles
  • Self-Discharge: 10% per month

Pros:

  • High discharge and charge currents.
  • Durable if maintained correctly.
  • Performs well in extreme cold.
  • Low cost.

Cons:

  • Low energy density (bulky).
  • Pronounced “memory effect” (needs periodic full discharge).
  • High self-discharge rate.
  • Environmental toxicity.

Ni-MH (Nickel-Metal Hydride) batteries were developed to address the shortcomings of NiCd. They offer about 20% more capacity in the same size and are more environmentally friendly.

Pros:

  • Higher energy capacity than NiCd.
  • Minimal memory effect.
  • Environmentally safe.

Cons:

  • Shorter overall service life than NiCd.
  • Lower temperature threshold.
  • Higher self-discharge (15–20% per month).

Lithium Batteries (Li-Ion, Li-Pol, LiFePO4)

This is where things get interesting for electric vehicles.

Li-Ion (Lithium-Ion) is the current industry standard, powering everything from smartphones to Tesla cars. They are lightweight and high-capacity but have limitations regarding temperature and current output.

Technical Characteristics:

  • Nominal Voltage: 3.6–3.7 V
  • Specific Energy: 110–243 Wh/kg
  • Life Cycle: ~600 cycles (to 80% capacity)
  • Self-Discharge: ~3% per month

Pros:

  • Highest energy density.
  • Negligible memory effect.
  • Very low self-discharge.

Cons:

  • Fire risk if overcharged or damaged.
  • Poor performance in sub-zero temperatures.
  • Generally lower discharge currents (unless using high-drain cells).
  • Requires a Battery Management System (BMS).
  • Capacity degrades over time (aging).

Li-Pol (Lithium-Polymer) batteries use a polymer electrolyte, allowing for flexible, thin, and lightweight “pouch” designs. They are popular in RC models and some e-bikes due to their high discharge rates.

Pros:

  • Extremely high energy density.
  • Flexible shapes and sizes.
  • Higher discharge rates than standard Li-Ion.

Cons:

  • Higher fire/explosion risk if punctured or mistreated.
  • Sensitive to deep discharge (below 3V).
  • More expensive and prone to “swelling.”

LiFePO4 (Lithium Iron Phosphate) is arguably the best choice for DIY e-bike enthusiasts. While slightly less energy-dense than Li-Ion, they are incredibly durable and safe.

Technical Characteristics:

  • Life Cycle: 2,000–7,000 cycles (extremely long-lived).
  • Service Life: Up to 15 years.
  • Operating Temperature: -30°C to +55°C.
  • Max Discharge Current: Up to 10C.

Pros:

  • Exceptionally long life.
  • Chemically and thermally stable (won’t catch fire).
  • Flat discharge curve (constant voltage until nearly empty).
  • Excellent cold-weather performance.

Cons:

  • Lower energy density (larger and heavier than Li-Ion for the same capacity).
  • Still requires a BMS.

Battery Comparison Table

To make this data easier to digest, I’ve compiled a comparison based on a theoretical 74V 32Ah battery pack. This allows us to compare weight, price, and longevity across different technologies.

As the table shows, Li-Ion 18650 cells offer the best price-to-weight ratio, which is why they are the standard for most commercial and DIY builds. LiFePO4 follows, offering better longevity at a slightly higher weight and price.

Conclusion

After weighing the factors, we have three main contenders. Here is how I rank them for my specific needs:

  1. LiFePO4 (Lithium Iron Phosphate): The clear winner for longevity and safety. If you plan to keep your e-bike for many years and ride in various weather conditions, the extra weight is worth the 10+ year lifespan.
  2. Li-Ion: The best balance for most riders, especially where weight and initial cost are the primary concerns.
  3. Li-Pol: Great for high-performance builds where weight is everything, but the safety risks and shorter lifespan make it less ideal for a daily commuter.

Living in Krasnodar, where summer temperatures regularly exceed +40°C, safety is a major concern. Standard Li-Ion and Li-Pol are more volatile in extreme heat. For my build, I’ve chosen prismatic LiFePO4 elements. They are increasingly affordable on AliExpress, and their long-term value is unbeatable.

If you live in a more temperate climate, Li-Ion is a fantastic choice—just ensure you have a good BMS and consider thermal insulation if you ride in the winter.

I hope this guide helps you in your own e-bike journey! Feel free to share this post or follow for more updates.

Thanks for your attention! :)