Battery Fundamentals

Your e-bike battery is the fuel tank of your electric conversion. Understanding the key specifications helps you choose a battery that provides the range, power, and lifespan you need.

Key Battery Specifications

Voltage (V)

What it means: The electrical pressure that pushes current through your motor
Common voltages: 36V, 48V, 52V, 72V

How voltage affects performance:

• Higher voltage = more speed and better hill climbing
• Lower voltage = longer battery life and lower cost
• Motor compatibility - voltage must match your motor specs

Voltage recommendations:

• 36V: Basic conversions, flat terrain, budget builds
• 48V: Most popular choice, good balance of performance and cost
• 52V: Higher performance, faster speeds, more expensive
• 72V: High-performance builds, steep hills, experienced builders

Capacity (Ah - Amp Hours)

What it means: How much energy the battery can store
Common capacities: 10Ah, 14Ah, 17.5Ah, 20Ah

How capacity affects range:

• Higher Ah = longer range but heavier battery
• Lower Ah = shorter range but lighter and cheaper
• Typical range: 20-60 miles depending on capacity and usage

Capacity recommendations:

• 10-12Ah: Short commutes (10-25 miles)
• 14-15Ah: Medium range (25-40 miles)
• 17-20Ah: Long range (40-60+ miles)
• 20+Ah: Extended touring, cargo hauling

Watt Hours (Wh)

What it means: Total energy storage (Voltage × Amp Hours)
Example: 48V × 14Ah = 672Wh

Why Wh matters:

• More accurate range predictor than Ah alone
• Easy comparison between different voltage batteries
• Legal limits - some areas restrict Wh capacity

Wh guidelines for range:

• 300-500Wh: 15-30 miles
• 500-700Wh: 25-45 miles
• 700-1000Wh: 40-65 miles
• 1000+Wh: 60+ miles

Battery Chemistry Types

Lithium-Ion (Li-ion)

Most common type for modern e-bikes

Advantages:

• High energy density (lightweight for capacity)
• No memory effect
• Low self-discharge rate
• Good temperature tolerance

Disadvantages:

• More expensive than older technologies
• Requires proper charging management
• Performance degrades in extreme cold

Best for: Most e-bike conversions

Lithium Iron Phosphate (LiFePO4)

Premium battery chemistry with enhanced safety

Advantages:

• Extremely safe and stable
• Long cycle life (2000+ charge cycles)
• Good high-temperature performance
• Very reliable

Disadvantages:

• Lower energy density (heavier)
• Higher upfront cost
• Lower voltage per cell

Best for: Long-term use, safety-critical applications, hot climates

Lead Acid (Sealed Gel/AGM)

Older technology still used in budget builds

Advantages:

• Very inexpensive
• Readily available
• Safe and stable

Disadvantages:

• Heavy weight
• Short cycle life (300-500 cycles)
• Poor cold weather performance
• Limited depth of discharge

Best for: Budget builds where weight isn't critical

Battery Life and Cycles

Understanding Cycle Life

What's a cycle: One complete discharge and recharge of the battery
Typical cycle life:

• Lithium-ion: 800-1000 cycles
• LiFePO4: 2000+ cycles
• Lead acid: 300-500 cycles

Factors Affecting Battery Life

Depth of Discharge (DoD):

• Shallow discharge (20-80%) = longer life
• Deep discharge (0-100%) = shorter life
• Optimal range: Keep battery between 20-80% when possible

Temperature:

• Moderate temps (60-80°F) = optimal life
• Extreme heat reduces capacity and life
• Extreme cold temporarily reduces capacity

Charging habits:

• Partial charges are better than full cycles
• Avoid leaving battery at 100% or 0% for extended periods
• Use appropriate charger designed for your battery

Extending Battery Life

Best practices:

• Charge after each ride rather than waiting for full discharge
• Store battery at 50-60% charge if not used for weeks
• Avoid extreme temperatures during charging and storage
• Use a quality charger with proper voltage and current limits

Try this: Use our Battery Life Planner to estimate how long your battery will last based on your usage patterns.

Battery Mounting and Integration

Mounting Styles

Frame-mounted batteries:

• Integrated into bike frame design
• Clean, professional appearance
• May require frame modifications

Rack-mounted batteries:

• Mounts on rear or front rack
• Easy to remove for charging
• Works with most bike frames

Bottle-mounted batteries:

• Fits in water bottle cage
• Easy installation and removal
• Limited capacity due to size constraints

Seat tube batteries:

• Mounts inside or on seat tube
• Good weight distribution
• May limit seat post adjustment

Removability Considerations

Removable batteries:

• Convenient for apartment charging
• Theft prevention
• Easy battery replacement

Fixed batteries:

• More secure mounting
• Cleaner appearance
• Requires bike storage near charging outlet

Charging Your Battery

Charger Specifications

Voltage matching: Charger voltage must match battery voltage
Current rating: Higher amperage = faster charging
Quality matters: Use chargers with safety certifications

Typical charge times:

• 2A charger: 5-8 hours for 10-14Ah battery
• 3A charger: 3-5 hours for 10-14Ah battery
• 5A charger: 2-3 hours for 10-14Ah battery

Charging Safety

Important safety rules:

• Never leave charging unattended overnight
• Charge in well-ventilated area away from flammable materials
• Stop using battery if it shows signs of damage or swelling
• Use only manufacturer-approved chargers

Signs of battery problems:

• Significant capacity loss (less than 70% of original)
• Physical damage or swelling
• Excessive heat during charging
• Error messages from charger

Battery Cost Considerations

Initial Purchase Price

• Budget Li-ion: $300-500 for 48V 10-14Ah
• Quality Li-ion: $500-800 for 48V 14-17Ah
• Premium LiFePO4: $800-1200 for 48V 14-20Ah

Cost Per Mile

• Calculate: Battery cost ÷ (range per charge × cycle life)
• Example: $600 battery, 40 miles/charge, 800 cycles = $0.019/mile
• Comparison: Often cheaper than gas per mile

Replacement Timeline

• Standard Li-ion: Replace after 3-5 years of regular use
• Premium LiFePO4: Replace after 5-8 years of regular use
• Usage dependent: Heavy daily use shortens lifespan

Battery Recommendations by Use Case

Daily Commuting (10-20 miles)

Recommended: 48V 14Ah Li-ion

• Capacity: 672Wh provides reliable range
• Charging: Charge nightly at home
• Lifespan: 3-4 years with daily use

Weekend Recreation (20-40 miles)

Recommended: 48V 17.5Ah Li-ion

• Capacity: 840Wh handles longer rides
• Charging: Charge after each ride
• Lifespan: 5-7 years with weekend use

Long Distance Touring (40+ miles)

Recommended: 52V 20Ah LiFePO4

• Capacity: 1040Wh for extended range
• Durability: Premium chemistry for reliability
• Lifespan: 8-10 years with proper care

Cargo/Heavy Duty Use

Recommended: 48V 20Ah LiFePO4

• High current capability: Handles power demands
• Durability: Withstands demanding use
• Safety: Most stable chemistry for high-power applications

Next Steps

Ready to size your battery? Use our Range Estimator to calculate how much capacity you need for your typical rides.

Looking at complete systems? Check our Best Kits 2025 guide for battery and motor combinations that work well together.

Quick Reference

Battery Sizing Quick Guide

Chemistry Comparison

Last updated: January 17, 2025