How to Size a Battery Storage System for Your EV Charging Station

Are you worried about your EV charging station’s battery storage system being too small to meet demand or too large, inflating project costs? Proper battery sizing is the cornerstone of a reliable, cost-effective commercial EV charging solution. A misstep in sizing can lead to power shortages, frustrated customers, or wasted investment. In this guide, we’ll show you how to size a battery for EV charging, ensuring your station delivers fast, efficient service while maximizing return on investment (ROI).

Why Correct Sizing Matters for Your EV Charging Station

Choosing the right battery storage system for your EV charging station is critical to avoid costly pitfalls. An undersized battery can’t handle peak demand, leading to slow charging speeds and unhappy users. An oversized battery, meanwhile, drives up costs without adding value. Industry data reveals that improper battery sizing can increase project expenses by up to 30%. For commercial operators, a well-sized battery storage for fast chargers optimizes ROI, ensures seamless user experiences, and keeps your station competitive in the growing EV market.

Key Parameters That Determine Battery Storage Size

To design an effective battery storage system for your EV charging station, you must evaluate several key parameters. These factors determine the capacity (kWh) needed to meet demand while staying cost-efficient. Below, we detail each parameter, including industry-standard reference values, and provide a table summarizing their impact.

1. Number of EV Chargers and Their Output

The power rating of each charger (e.g., 22 kW, 60 kW, 150 kW) and the number of chargers operating simultaneously define peak power demand. For example, four 60 kW fast chargers running at once require up to 240 kW.

Industry Reference: Most commercial EV charging stations deploy 2–8 chargers, with fast chargers (50–150 kW) making up 70% of installations.

2. Average Daily Charging Sessions

The frequency of charging sessions (high vs. low) affects the battery’s depth of discharge (DoD), or how much capacity is cycled daily. High-frequency stations require robust batteries to handle multiple cycles.

Industry Reference: Typical EV charging stations operate at 60–80% DoD, with 10–30 daily sessions per charger.

3. Desired Backup Duration or Peak Shaving Window

How long must the battery support charging? A 1-hour peak shaving window may suffice for busy periods, while off-grid or high-demand stations may need 4+ hours of backup.

Formula: Required capacity (kWh) = Power (kW) × Duration (h). 

For example, 240 kW for 2 hours = 480 kWh.

Industry Reference: Most stations target 1–3 hours of peak shaving, requiring 100–500 kWh.

4. Grid Constraints and Interconnection Limits

Grid limitations, such as restricted power supply or high demand charges, often necessitate a battery storage system. Batteries can offset peak loads, reducing utility costs.

Industry Reference: Over 50% of urban EV charging stations face grid constraints, with batteries managing 20–40% of peak demand.

5. Future Scalability

Plan for future growth. Will you add more chargers later? Modular battery storage for fast chargers allows easy expansion without over-investing upfront.

Industry Reference: Scalable systems typically support 25–50% capacity increases via parallel modules.

Parameter Impact on Battery Capacity

The table below illustrates how each parameter influences battery sizing for your EV charging station:

Battery Sizing Examples for EV Charging Stations

To demonstrate how to size a battery for EV charging, we’ve outlined two real-world scenarios. These examples show how parameters translate into practical commercial EV charging solutions, helping you visualize the right battery storage system for your project.

Case 1: Small Retail Parking Lot

• Setup: 4 × 22 kW AC chargers.
• Usage: 20 daily sessions, averaging 1 hour each.
• Requirements: Support peak demand for 2 hours, minimal grid constraints.
• Recommended Battery: 50–100 kWh, sufficient for daily cycles and cost-effective operation.
• Optimization: Pair with time-of-use tariffs to reduce electricity costs by up to 15%.

Case 2: Urban Gas Station Retrofit

• Setup: 2 × 150 kW DC fast chargers.
• Usage: Peak operation for 2 hours during rush periods.
• Requirements: Manage grid limits and ensure fast charging reliability.
• Recommended Battery: 300–400 kWh, supporting high-power demand and peak shaving.
• Optimization: Integrate solar panels or dynamic pricing to save 20–30% on energy costs.

Battery Sizing Checklist for Your Project

Use this checklist to ensure you're considering all key factors for accurate sizing:

Inventory of Charging Equipment

• Total number of chargers on-site
• Output rating per charger (kW)

Energy Usage Profile

• Daily charging sessions per charger
• Average session duration
• Total daily kWh demand

Site Power Availability

• Grid connection capacity
• Existing peak demand constraints

Required Backup or Load Shifting Time

• Target duration to support loads via battery storage
• Whether you need full backup or peak shaving

Depth of Discharge (DoD) Target

• Preferred battery utilization vs. system lifespan tradeoff

Scalability Requirements

• Future plans for charger expansion
• Modular add-on compatibility

Smart Control Systems

• Need for intelligent BMS
• Integration with EMS or remote monitoring platforms

Environmental Considerations

• Indoor vs. outdoor installation
• Temperature range and IP rating needs

Why Choose a Custom Battery Storage Provider

Generic battery storage systems often overlook site-specific needs, such as layout, grid access, or charger compatibility. A custom battery storage for fast chargers ensures safety, cost-efficiency, and long-term reliability. At ACE Battery, we provide:

• Tailored capacity recommendations based on your project’s unique needs.
• Detailed design blueprints for seamless integration.
• Integrated battery, Battery Management System (BMS), and Energy Management System (EMS) solutions.
• Turnkey installation and ongoing support.

Our customized commercial EV charging energy storage solutions have helped clients reduce energy costs by up to 25% while ensuring 99.9% uptime. Let us optimize your EV charging station for performance and profitability.

Conclusion: Power Your EV Charging Station with Confidence

A properly sized battery storage system is the foundation of a successful EV charging station. Don’t let under- or over-sizing compromise your project’s efficiency or profitability. By carefully evaluating your station’s needs and partnering with experts, you can ensure reliable performance and maximum ROI.

Contact ACE Battery today for a personalized battery sizing plan and quote within 24 hours. Take the first step toward a future-proof commercial EV charging solution!