The Battery Sizing Guide: From Duty Cycle to kWh Selection
In the first two installments of The Battery Sizing Guide, you established a data-driven foundation for your electrification project. In Part 1, you defined your application’s fundamental power (kW) and energy (kWh) needs. In Part 2, you mapped its unique duty cycle — the real-world pattern of how that power and energy are used over time.
You have all the essential data. Now what?
In this final segment of The Battery Sizing Guide, we’ll show you how to put it all together. We will walk you through the process of translating your detailed load profile and duty cycle into a specific kilowatt-hour (kWh) requirement, empowering you to select the right battery for your application.
You have a clear profile of your equipment's power demands and a detailed map of its duty cycle. Now it’s time to use that data to answer the ultimate question: How much battery capacity do you actually need?
The Sizing Formula: Turning Data Into kWh
The process of determining your energy requirement begins with a simple formula. You use the data you’ve gathered to find the average power your machine consumes during operation and multiply it by the required runtime.
For example, if your duty cycle analysis shows that your machine draws an average of 2 kW of power over a required 4-hour runtime, your baseline energy need is 8 kWh. This simple calculation is the crucial starting point that gets you in the right ballpark.
Adjusting for Real-World Factors
Your baseline kWh number is the foundation, but it isn’t the final answer. To make sure your battery delivers the performance your customers expect on the hottest days and toughest jobs, and for years to come, we need to adjust for a few key variables. Think of this process like applying a safety factor in mechanical engineering — you design for the expected load, then add a buffer to handle the unexpected.
Depth of Discharge (DoD): No battery delivers 100% of its rated capacity. The DoD is the percentage of the battery’s energy you can actually use. While a lead-acid battery may only have a DoD of around 60%, modern lithium-ion batteries, like Vanguard commercial batteries, offer a much higher usable capacity — often over 90%. This high DoD means you can select a smaller, lighter battery to do the same amount of work.
Runtime Buffers: A safety factor is crucial for accounting for real-world variability, from different operator behaviors to rough conditions like muddy terrain. Building in a small buffer (e.g., 10%–20%) ensures that the equipment can handle these tougher-than-average days without running out of power.
Long-Term Degradation: Many people fear battery degradation because of their experience with cell phones. However, the batteries in commercial equipment are engineered for a much longer and more robust service life. While all batteries lose some capacity over thousands of cycles, the degradation in a high-quality, properly maintained battery is far less than most people think. Factoring a small buffer for this long-term degradation into your final calculation is the practical way to ensure the machine meets performance expectations for years to come.
Why Right-Sizing Is Crucial: The Ultimate Balancing Act
Using your data and these real-world factors to "right-size" your battery is one of the most critical steps in your entire project. It's a balancing act between three competing factors:
Runtime: The battery must have enough capacity for your customer to get their job done effectively.
Cost: Using an oversized battery, often the result of a customer saying "I need it to run for eight hours straight," is the fastest way to make a product too expensive to compete in the marketplace.
Weight: Unnecessary battery capacity adds weight, which can impact the machine's performance, handling and usability.
Right-sizing isn't just about making the math work; it's about delivering a superior user experience. A properly electrified machine is often objectively better than its gas-powered predecessor due to "soft factors" like less noise, less vibration and instantaneous power. Nailing the runtime and performance allows these benefits to shine through.
Your Partner in Optimization
Navigating the final trade-offs between runtime, cost and weight can feel daunting, but you don't have to do it alone. At Vanguard, we act as a true integration partner by providing a complete system of batteries, motors and motor controllers that are designed to work together seamlessly.
This system approach reduces complexity and shortens your time to market. Our application experts and Battery Technology Partners work with you to analyze your data and select the optimal power solution, allowing your team to focus on what it does best: designing and building world-class equipment.
The Journey to Electrification
The three articles in The Battery Sizing Guide have walked you through a proven, data-driven process. You started by defining your loads, then mapped your duty cycle, and have now translated that data into a specific kWh requirement.
The journey to electrification isn't about guesswork; it's a methodical process of replacing assumptions with data to create a product that is powerful, efficient and profitable. When you're ready to take the next step, our team is here to help you get started.
