Beyond Price: How to Evaluate cells Value by LiFePO4 Datasheet Metrics
LiFePO4 datasheet metrics: When buying LiFePO4 (Lithium Iron Phosphate) battery cells, many people only look at the price. But just going for the cheapest option can lead to problems later — like poor performance, short battery life, or safety risks.
If you want a battery that’s reliable, lasts long, and suits your needs, you must check the datasheet carefully. The datasheet is like a report card — it tells you what the battery can really do.
In this blog, we’ll explain how to read a LiFePO4 battery datasheet in simple words and how to use that information to find the best value — not just the lowest price.
✅ What Is a Battery Datasheet?
A battery datasheet is a technical document provided by the manufacturer. It includes important numbers and details that tell you how the battery works — like how much power it gives, how long it lasts, how hot it can get, and how safe it is.
If you can read these details, you can avoid low-quality or fake cells and choose the right one for your project.
🔍 Important LiFePO4 Datasheet Metrics (Explained in Simple Words)
Here are the main things to look for in a datasheet and what they really mean:
⚡ 1. Nominal Capacity (Ah)
- What It Means: This tells you how much energy the battery can store.
- Measured In: Ampere-hours (Ah)
- Why It Matters: The higher the number, the more energy the cell can provide before it needs charging again.
- Tip: Make sure it matches what you need. For example, a 100Ah battery gives more backup than a 50Ah battery.
🔁 2. Cycle Life
- What It Means: How many times the battery can be charged and discharged before it loses most of its capacity.
- Measured As: Number of full cycles until the battery drops to 80% of its original capacity.
- Why It Matters: More cycles = longer life. A battery with 4,000 cycles will last much longer than one with 1,000 cycles.
📝 Always check the conditions under which the cycle life was tested — at what temperature, at what depth of discharge (DOD), and at what current rate?
🔌 3. Internal Resistance (IR)
- What It Means: How hard it is for electricity to move inside the battery.
- Measured In: Milliohms (mΩ)
- Why It Matters: Lower resistance is better. It means the battery can deliver power more easily and stays cooler.
- Tip: Batteries with high internal resistance waste energy and get hot during use.
🔋 4. Discharge Current (Continuous & Peak)
- What It Means:
- Continuous discharge is the amount of current the battery can give steadily.
- Peak discharge is the highest current it can give for a short time.
- Why It Matters: If you need the battery to run high-power devices (like motors or inverters), it must handle high discharge currents without damage.
🔺 Choosing a battery with low discharge ratings for high-load projects can lead to overheating and failure.
🔍 5. Charge Voltage and Cutoff Voltage
- What It Means: These are the highest and lowest voltages at which the battery should operate.
- Why It Matters: If the voltage goes outside this range, the battery can get damaged or unsafe.
- Tip: Make sure your charger and BMS (Battery Management System) follow these limits.
🌡️ 6. Operating Temperature Range
- What It Means: The safe temperature range for charging and discharging the battery.
- Why It Matters: If the battery is used in very hot or cold conditions outside the range, it might stop working or get damaged.
- Typical Range:
- Charging: 0°C to 45°C
- Discharging: -20°C to 60°C
❄️ Never charge LiFePO4 cells below 0°C — it can cause lithium plating, which damages the cell permanently.
🔋 7. Self-Discharge Rate
- What It Means: How quickly the battery loses charge when it’s not being used.
- Why It Matters: A good-quality LiFePO4 battery should hold charge for months. If it discharges quickly, it may be old or low quality.
✅ 8. Certifications
- What It Means: These are official approvals showing the battery has passed safety and quality tests.
- Common Certifications:
- UN38.3 – Safety for transport
- UL – General safety
- CE – European safety compliance
- IEC62619 – Safety for battery systems
- Why It Matters: Certified batteries are safer to use and often required for shipping or installing in regulated systems.
💡 Real-World Example: Why Price Isn’t Everything
Let’s say you are comparing two cells:
| Feature | Cell A | Cell B |
|---|---|---|
| Price per Cell | $85 | $65 |
| Capacity | 100Ah | 100Ah |
| Cycle Life | 4,000 cycles | 2,000 cycles |
| Usable Energy | 100Ah × 3.2V × 80% × 4,000 = 1,024 kWh | 512 kWh |
| Cost per kWh | $0.083 | $0.127 |
📌 Conclusion: Even though Cell B is cheaper at first, Cell A gives twice the energy over its life and ends up costing you much less in the long run.
🚨 Warning Signs in a Bad LiFePO4 datasheet metrics
- ❌ Missing test conditions (e.g., no info on how cycle life was tested)
- ❌ Unrealistic claims like “10,000 cycles” with no proof
- ❌ No certifications or safety reports
- ❌ Different values shown for the same model on different documents
💬 FAQs about LiFePO4 datasheet metrics
Q1: What if the LiFePO4 datasheet has no cycle life info?
A: That’s a red flag. Reliable suppliers always share cycle life test results.
Q2: Can I test internal resistance myself?
A: Yes. Use a battery IR tester. You can compare it with the datasheet to check if it matches.
Q3: Why does the same capacity battery have different prices?
A: Because of quality, grade (A or B), certifications, and performance specs. Price doesn’t tell the full story.
🏁 Final Thoughts
When buying LiFePO4 batteries, don’t just ask, “How much does it cost?”
Instead, ask:
- How long will it last?
- Is it safe?
- Will it work well in my system?
- Does the datasheet match the performance I need?
📘 The LiFePO4, battery datasheet, battery safety, battery grading, energy storage, EV batteries, cycle life, internal resistancet gives you the answers. Learn how to read it — and you’ll make better, safer, and more cost-effective decisions.
Demystifying LiFePO4 Battery Testing: How Manufacturers Grade Their Cells
LiFePO4 battery testing: LiFePO4 batteries have become the backbone of energy storage systems, from solar power banks to electric vehicles. But did you know that behind every “Grade A” label is an extensive, complex process of testing, sorting, and grading? This blog post takes you inside the factory to reveal how manufacturers test LiFePO4 cells, what parameters matter most, and why standardized grading remains a challenge.
Introduction to Battery Manufacturing QC for LiFePO4 Battery Testing
In any reputable LiFePO4 cell factory, Quality Control (QC) is the beating heart of the operation. The manufacturing process includes multiple checkpoints — from raw material inspection to final cell testing. Even the best production lines produce cells with slight variations. These variations affect performance, safety, and lifespan, which is why proper grading is essential.
Grading helps ensure that cells with similar performance characteristics are grouped together. This is vital for applications like energy storage systems (ESS), where mismatched cells can cause premature failure or reduced efficiency.
LiFePO4 Battery Testing Parameters: What Gets Checked?
Let’s break down the most critical parameters manufacturers measure when grading LiFePO4 cells.
1. Capacity (Ah)
Capacity is the total amount of charge a cell can store, typically measured in ampere-hours (Ah). Manufacturers run charge-discharge cycles to verify that the cell meets or exceeds its rated capacity — usually within ±2% for Grade A cells. Cells that fall slightly below the spec can get downgraded to Grade B or C.
2. Internal Resistance (IR)
Internal resistance affects how well a battery can deliver current. High IR means greater energy losses and more heat during use. Cells with lower IR are preferred for applications requiring high power output. Manufacturers test IR at different temperatures to ensure stability.
3. Voltage Matching
Cells are sorted based on their open-circuit voltage (OCV) to ensure that packs built from multiple cells stay balanced. Cells with mismatched voltages can lead to uneven charge/discharge cycles and reduce overall pack life.
4. Self-Discharge Rate
A cell’s self-discharge rate determines how quickly it loses charge when not in use. Excessive self-discharge indicates internal defects or impurities, which can compromise performance and safety.
Cycle Life Testing Protocols: How Long Will It Last?
One of the biggest selling points of LiFePO4 is its long cycle life — often 2,000–6,000 cycles. But how is this tested?
Manufacturers perform accelerated cycle life tests. Cells are charged and discharged repeatedly at defined C-rates (charge/discharge rates) and ambient temperatures. They measure capacity fade over time. A high-quality Grade A cell should retain at least 80% of its original capacity after the specified number of cycles.
Due to time constraints, manufacturers often rely on statistical sampling and predictive modeling rather than testing every cell for thousands of cycles.
Safety Tests: Beyond Performance
LiFePO4 is one of the safest lithium-ion chemistries, but that doesn’t mean safety tests are skipped.
Common safety tests include:
- Overcharge Test: The cell is charged beyond its maximum voltage to check for thermal runaway or swelling.
- Over-Discharge Test: The cell is deeply discharged to see if it can recover without damage.
- Short Circuit Test: The terminals are shorted under controlled conditions to check heat generation and structural integrity.
- Temperature Tests: Cells are exposed to extreme hot and cold to ensure stable performance across operating ranges.
Cells that fail safety tests are immediately rejected or downgraded for less demanding applications.
The “Defect Rate” and How Grade B/C Cells Are Created
No production line is perfect. Even leading manufacturers have a defect rate — usually 3–5% — where cells fall outside the ideal performance window.
Grade B cells: Slightly lower capacity or higher IR than Grade A, but still usable for less critical applications like budget power banks or backup systems.
Grade C cells: Significant deviations or borderline defects. Often sold at a deep discount for non-critical uses or recycling. These should never be used in high-demand or mission-critical projects.
Some unscrupulous sellers remarket Grade B or C cells as Grade A, so it’s crucial to buy from trusted suppliers with traceable testing data.
LiFePO4 Battery Testing: Why Standardized Grading is a Challenge
One frustrating reality in the LiFePO4 market is the lack of a global standard for grading. Different factories may use slightly different thresholds for what they call Grade A, B, or C.
Factors like:
- Local production tolerances
- Variations in test equipment
- Sampling size
- Batch-specific conditions
…all mean that “Grade A” from one supplier might be closer to “Grade B” by another’s standards.
For buyers, this makes third-party testing and working with reputable suppliers essential. A cell’s data sheet should always come with original test reports showing capacity, IR, and other key parameters.
Final Thoughts: Stay Informed, Source Smart
Demystifying LiFePO4 cell grading is about understanding the science behind your battery pack. When you know what goes into the tests — capacity, IR, voltage, cycle life, and safety — you can better evaluate what you’re buying.
✅ Always ask for factory test reports.
✅ Buy from suppliers who are transparent about their QC processes.
✅ Match your project’s needs with the right cell grade.
A few extra dollars spent on verified Grade A cells can save you massive headaches, costly replacements, or even safety risks down the line.
LiFePO4 Battery Testing FAQs
Q: How do I know if a LiFePO4 cell is really Grade A?
A: Always request factory test reports showing capacity, internal resistance, voltage, and cycle life data.
Q: Are Grade B cells safe to use?
A: They can be safe for low-demand applications but avoid using them in critical systems like off-grid solar storage or EVs.
Q: Why do some sellers mislabel cells?
A: To maximize profit. Unscrupulous sellers can mix Grade B/C cells into Grade A batches to cut costs.
The Hidden Dangers of Low-Grade LiFePO4 Cells: Don’t Get Scammed!
The growing popularity of LiFePO4 (Lithium Iron Phosphate) batteries in solar energy storage, RVs, and off-grid setups has brought a flood of suppliers into the market. It’s tempting, especially for DIYers and budget-conscious buyers, to grab the cheapest deal. But beware — that bargain pack of cells labeled “Grade A” at suspiciously low prices might actually be low-grade or even rejected cells. The short-term savings could cost you big in the long run. how to protect from Battery Scam?
The Trap: Why Cheap Batteries Can Cost You More
There’s a reason reputable suppliers and certified manufacturers charge more for Grade A LiFePO4 cells. High-quality cells are rigorously tested for consistency in capacity, internal resistance, cycle life, and safety. Low-grade or Grade C cells often fail these tests — they’re the factory rejects, excess stock, or even refurbished cells passed off as new.
Unscrupulous sellers know that most buyers can’t test cells themselves. They slap a “Grade A” sticker on low-quality cells and move inventory fast. Once the battery pack fails or causes problems, it’s too late.
Performance Issues: The Hidden Cost of Low-Grade Cells
1. Unexpected Capacity Drops:
Low-grade cells often have inconsistent capacity ratings. You might think you’re getting 100Ah, but in real-world use, you may only get 70–80% of the advertised capacity — if that.
2. Inconsistent Power Output:
Cells with mismatched internal resistance or degraded chemistry can’t deliver stable power. You’ll notice fluctuations, poor performance under load, or even sudden shutoffs — not ideal if you rely on your batteries for critical energy needs.
Safety Hazards: A Risk You Shouldn’t Ignore
LiFePO4 batteries are known for their thermal stability — they’re among the safest lithium chemistries out there. But when cells are low-grade, damaged, or have internal defects, safety goes out the window.
Overheating & Swelling: Poor-quality cells are more prone to swelling due to gas buildup. They can overheat during charging or discharging, increasing the risk of thermal runaway.
Shortened Lifespan and Financial Losses
Imagine spending hundreds or thousands of dollars to build or buy a battery bank, only to have cells fail after a few months. Low-grade cells can lose capacity rapidly, dropping below usable levels in a fraction of the cycles you’d get from genuine Grade A cells.
What’s worse, a single bad cell can drag down an entire battery pack — meaning you may have to replace the whole thing. So, that “cheap” deal can turn into double or triple the cost over time.
How to Protect Yourself: Smart Buying Steps
Don’t get scammed — here’s how to safeguard your project and your wallet:
✅ Do Your Due Diligence: Research suppliers thoroughly. Check reviews, forums, and independent test reports.
✅ Verify Supplier Claims: Reputable sellers will share the factory test reports, including capacity, internal resistance, and cycle life data. Don’t hesitate to ask.
✅ Look for Certifications: Ensure the cells meet international safety standards like UN38.3, IEC, or UL certifications.
✅ Inspect on Arrival: Check the physical condition of cells. Look for dents, swelling, corrosion, or mismatched labels.
✅ Run Your Own Tests: If you have the tools, test cells for capacity and internal resistance before building your pack.
✅ Work with Trusted Partners: Sometimes it’s worth paying a local representative or battery expert to vet suppliers and inspect shipments, especially for bulk orders.
Real-World Examples: When Cheap Batteries Go Bad
🔍 Case in Point:
A small off-grid community bought a pallet of “Grade A” LiFePO4 cells from an unknown online supplier. Within six months, over 40% of the cells were swollen and underperforming. When they tried to claim a warranty, the seller disappeared. They ended up paying twice — once for the junk cells, and again for new, certified replacements.
🔍 Another Example:
A DIYer on a popular solar forum shared photos of cells they’d bought at a discount. They discovered old weld marks under the heat shrink — the cells were clearly recycled from old packs. This can pose both performance and safety issues.
Final Thoughts: Spend Smart, Not Cheap
LiFePO4 batteries are a great investment — but only if you buy quality. When it comes to energy storage, you truly get what you pay for. A cheap battery today can become a costly, even dangerous headache tomorrow.
So, be cautious. Ask questions. Demand data. And when in doubt, remember: a trusted supplier might cost more upfront, but they’ll save you thousands in headaches down the road.
Frequently Asked Questions
Q: Are all Chinese LiFePO4 cells low-grade?
A: No! China is the world’s leading manufacturer of high-quality LiFePO4 cells. The key is buying from reputable factories and verified suppliers.
Q: How can I tell if a cell is Grade A or C?
A: Without testing, it’s hard. That’s why factory test reports, supplier transparency, and independent verification matter so much.
Q: Is buying refurbished or used cells ever worth it?
A: For non-critical applications, maybe. But always expect lower performance and a shorter lifespan — and never use them for applications where reliability is crucial.
Charging Temperature: The Overlooked Factor in Battery Datasheets
Charging temperature for batteries: When you read a lithium-ion cell datasheet, you’ll usually find a line that states:
“Operating Temperature: -20°C to 60°C.”
Most people take this to mean they can safely charge and discharge the battery anywhere within this range. But here’s the catch — this ‘operating temperature’ often applies only to discharge. In reality, charging temperature limits are much narrower, and charging a battery at too low a temperature can lead to permanent damage, poor performance, or even safety hazards.
Let’s unpack why charging temperature is so critical — and why most cell datasheets don’t clearly show the minimum or maximum charging current at low temperatures.
Why Temperature Matters More for Charging than Discharging
Chemical Reactions Are Temperature Sensitive
Batteries store and release energy through electrochemical reactions. When discharging, the battery’s internal resistance and chemical kinetics can handle lower temperatures reasonably well — albeit with reduced capacity.
But charging is different: at low temperatures, the lithium ions move more slowly and can deposit as metallic lithium on the anode surface instead of intercalating into the graphite layers. This is called lithium plating, and it’s a big problem.
What Is Lithium Plating — and Why Should You Care?
- Safety Risk: Plated lithium can form dendrites that pierce the separator, leading to internal short circuits.
- Capacity Loss: Once lithium plates, it often cannot be recovered, permanently reducing battery capacity.
- Performance Issues: Cells with lithium plating can show increased impedance and reduced power output.
In short, charging at temperatures below the manufacturer’s recommended minimum can destroy your battery, even if it works fine during discharge.
What Datasheets Usually Show (and What They Don’t)
Typical ‘Working Temperature Range’
Most cell datasheets provide a simple table:
| Parameter | Range |
|---|---|
| Operating Temperature | -20°C to 60°C |
| Storage Temperature | -20°C to 45°C |
Here’s the issue:
- The ‘Operating Temperature’ mostly reflects the discharge range, since discharging is more forgiving.
- The recommended charging temperature range is narrower, often 0°C to 45°C for typical lithium-ion cells.
- Many datasheets don’t list charging current limits at specific low temperatures, which can mislead inexperienced designers or end-users.
Why Charging Current Specs Are Missing
There are a few reasons:
✅ Simplicity: Datasheets are general-purpose and aim to cover a wide range of use cases.
✅ System-Level Responsibility: It’s expected that system integrators will design a Battery Management System (BMS) to enforce proper charging limits.
✅ Testing Constraints: It’s impractical for cell makers to test and specify safe charge currents for every temperature point.
However, high-quality battery packs, EVs, or energy storage systems will always have a BMS with temperature sensors that adjust or cut off charging below safe levels.
How to Interpret the Datasheet Correctly
When you see:
“Operating Temperature: -20°C to 60°C”
Remember:
✅ Discharge: -20°C to 60°C is possible.
✅ Charge: Typically 0°C to 45°C.
Always check if the datasheet has a line like:
“Charging Temperature: 0°C to 45°C”
or a separate graph showing charging current vs. temperature. If it doesn’t, follow standard battery chemistry best practices — and build your BMS to protect the cells.
Best Practices for Safe Charging at Low Temperatures
- Use a Good BMS: It must prevent charging below the minimum safe temperature (often 0°C).
- Pre-Heat When Necessary: In cold climates, electric vehicles and energy storage systems use heaters to bring battery packs up to a safe charging temperature.
- Reduce Charge Current: If you must charge slightly below the recommended temperature, reduce current to mitigate lithium plating risk — but always follow manufacturer guidance.
- Monitor and Test: In critical applications, add redundant sensors and logs to track battery health.
Final Thoughts
Charging temperature is often overlooked — until it’s too late. Understanding that the ‘working temperature’ range in a cell datasheet is usually for discharge, not charge, is key to protecting battery performance and lifespan.
Always design your system to account for real-world conditions, and never assume that what works for discharge is safe for charge. After all, a healthy battery is a happy battery — and it all starts with respecting temperature limits.
FAQ: Charging Temperature for Batteries
Q1: Why do manufacturers focus more on discharge temperature?
Discharging is generally safer across wider temperatures, while charging at low temperatures can cause irreversible damage. So the ‘headline’ working range is more about discharge capability.
Q2: Can I charge a lithium-ion battery at -10°C if I use a very low current?
In theory, slower charging reduces plating risk, but it’s still not recommended without manufacturer approval. Always stick to the specified minimum charging temperature.
Q3: How do electric vehicles handle low-temperature charging?
Most EVs have battery heaters that pre-warm the cells to reach a safe temperature range before fast charging begins.
Q4: Does fast charging make the problem worse?
Absolutely. Higher currents increase the risk of lithium plating at lower temperatures. Smart BMS systems reduce charge rates or stop charging altogether if it’s too cold.
From EV to Home Storage: The Promise of Second-Life Batteries and the Role of SOH
When an electric vehicle (EV) battery no longer delivers the range you expect, is it truly the end of the road? Not necessarily! Welcome to the world of second-life batteries applications, where used EV batteries get a new lease on life powering our homes, businesses, and communities.
In this post, we’ll explore how State of Health (SOH) plays a crucial role in unlocking this sustainable energy solution.
Why Do EV Batteries Reach “End of Life”?
EV batteries typically reach their End of Life (EOL) for vehicle use when their capacity drops to around 70–80% of their original value. While this means they can’t reliably provide the range needed for daily driving, they still hold a significant amount of usable energy.
This is where the concept of second-life batteries comes in — putting these batteries to work in less demanding environments, like stationary battery energy storage systems.
What is a Second-Life Battery?
A second-life battery is a battery that has completed its first life in an electric vehicle and is repurposed for another application. Instead of sending it straight to recycling, these batteries can serve in home energy storage, backup power systems, or grid-scale applications.
Repurposing extends the overall lifespan of the battery materials, reduces waste, and makes clean energy storage more affordable.
The Role of SOH in Second-Life Battery Applications
State of Health (SOH) is the single most important metric for deciding whether a used battery is suitable for a second life. SOH indicates how much usable capacity and performance a battery still has compared to its original specification.
Without accurate SOH data, integrating second-life batteries into energy storage systems would be risky. A battery that looks fine externally might not hold a charge effectively — or worse, it could pose safety risks.
That’s why reputable second-life projects rely on robust SOH testing and screening processes. This ensures that only safe, reliable batteries find a second home.
Second-Life Batteries for Home Energy Storage
One of the most promising uses for second-life batteries is home energy storage. With rooftop solar becoming more common, many homeowners want to store excess solar energy for use at night or during power outages.
Second-life batteries can be an affordable alternative to brand-new battery systems. Here’s why they make sense:
- Lower upfront cost: Second-life batteries are cheaper than new ones.
- Sustainable use of resources: Reusing batteries delays recycling, saving the energy and emissions needed to produce new cells.
- Adequate performance: Home energy storage is less demanding than powering a vehicle — fluctuations in capacity or power delivery are more manageable.
Challenges of Second-Life Batteries
Of course, second-life battery applications are not without challenges.
✅ Variation in SOH: Each battery pack will have a unique SOH, so grading, sorting, and system design are crucial.
✅ Warranty & standards: Consumers want to know their storage system is safe and reliable. Clear standards for SOH testing and certification are still evolving.
✅ Safety: A degraded battery needs to be properly managed by a Battery Management System (BMS) to prevent thermal issues.
How SOH Testing Works
Evaluating SOH involves:
- Capacity tests: Measuring the charge the battery can hold.
- Internal resistance checks: Higher resistance indicates aging.
- Visual & diagnostic inspections: Identifying any physical damage or irregularities.
Advanced diagnostic tools and algorithms make it possible to test large numbers of used EV batteries quickly and reliably, paving the way for scalable second-life applications.
A Step Toward a Circular Battery Economy
By giving EV batteries a second life, we’re taking a big step toward a more circular economy for batteries. Instead of a single-use model, we maximize the value of the raw materials and reduce the demand for new mining.
This approach helps the clean energy transition become even more sustainable and cost-effective for everyone.
Final Thoughts
Second-life battery applications are an exciting example of how we can combine smart technology, sustainability, and practical economics. Next time you think your EV battery is ready for retirement, remember: with the help of accurate SOH measurement, it might just be ready to power your home instead.
FAQs: Second-Life Batteries & SOH
Q1: How long do second-life batteries last?
Second-life batteries can last 5–10 years or more in stationary applications, depending on their SOH and how they’re used.
Q2: Are second-life batteries safe for home use?
Yes — when properly tested for SOH, repurposed batteries are safe for less demanding energy storage applications. Always choose reputable suppliers with strong testing and BMS controls.
Q3: How is SOH measured for second-life batteries?
SOH is measured through capacity testing, resistance checks, and advanced diagnostics to ensure the battery still performs reliably.
✅ Battery Cycle Standards Explained: SOH, DOD, and EOL — What Do They Really Mean?
Battery Cycle Standards: When search for batteries — whether for EVs, solar storage, or backup — you’ll see specs like “Cycle Life: 6,000+ cycles”.
But did you know these numbers can mean totally different things depending on how they’re tested?
Cycle life means nothing without knowing whether it’s tested by SOH, DOD, or EOL.
Understanding Battery Cycle Standards helps you compare apples to apples and avoid expensive mistakes.
⚡ What Is a Battery Cycle?
A battery cycle = fully charged + fully discharged once.
🔍 Tip: Partial discharges count too! For example, discharging to 50% twice equals one full cycle.
✅ Battery Cycle Standards SOH, DOD, and EOL — Your Key Terms
🟢 State of Health (SOH)
Shows the battery’s “health” compared to new.
- Starts at 100% when new.
- Drops as the battery ages.
When SOH drops to 80% or 70%, that’s usually considered End of Life (EOL).
🟢 Depth of Discharge (DOD)
Shows how deeply you use the battery before recharging.
- 100% DOD: full drain
- 80% DOD: partial drain
- Shallower DOD = longer life
👉 Example: If your battery is 100Ah and you use 80Ah before recharging, that’s 80% DOD.
🟢 End of Life (EOL)
The point when the battery no longer delivers acceptable performance.
Most specs define EOL as when capacity drops to 70% or 80% of original.
🔬 Why Different Battery Cycle Standards?
Not all manufacturers test the same way.
- Some test at shallow DOD to show higher numbers.
- Some stop tests when SOH drops a little.
- Some push the cell until true EOL for realistic numbers.
One battery’s “5,000 cycles” at SOH may mean just 4,000 in real use!
🗂️ Example: Same Cells, Different Specs
One company’s 3.2V 100Ah cells:
| Model | Test Standard | Cycle Life | Test Conditions |
|---|---|---|---|
| A | 80% SOH | 6,000+ | @ 25°C |
| B | 70% EOL | 8,000+ | @ 25°C |
| C | 80% DOD | 4,000+ | @ 25°C |
✅ Model A: Good initial health — but real EOL cycles likely ~5,000–5,400.
✅ Model B: Tested to true EOL — best for planning real use.
✅ Model C: Partial discharge test — lifespan drops if you run deeper DOD.
🔑 Quick Conversion Guide
| Declared Standard | Approx. Equivalent in EOL | Approx. Equivalent in SOH | Approx. Equivalent in DOD |
|---|---|---|---|
| SOH (e.g. 80% SOH) | –10% to –20% fewer cycles | Same | Depends on DOD used |
| EOL (e.g. 70% EOL) | Same | +10% to +20% more | Depends on DOD |
| DOD (e.g. 80% DOD) | –5% to –15% fewer at 100% DOD | Lower than SOH | Same |
✅ Always check: Test temp, DOD, current rates, EOL %!
✅ Which Standard Should You Trust?
🟢 EOL is most realistic for real-world use.
🟢 DOD is useful for estimating lifespan based on how you operate.
🟢 SOH is fine for lab data but doesn’t guarantee real-life lifespan.
Always prioritize EOL cycles tested at your expected DOD.
✅ Frequently Asked Questions (FAQ)
Q1: What is SOH on my spec sheet?
SOH is your battery’s health compared to new. A new battery is 100% SOH.
Q2: Why does my supplier show different cycle numbers for the same capacity?
They tested under different standards — SOH, DOD, or EOL. Always compare the same standard!
Q3: How does DOD affect cycle life?
Deeper DOD (e.g. 100%) = fewer cycles. Shallower DOD (50–80%) = more cycles.
Q4: Which cycle number should I plan my project on?
Always use EOL-tested cycles at your expected DOD. This gives you a realistic end-of-life cost forecast.
Q5: What should I ask my supplier?
✅ Test temperature & current
✅ DOD used
✅ EOL percentage
✅ Full cycle charts
✅ Warranty details
🔚 Final Thoughts
Battery cycle standards aren’t a gimmick — they’re a vital clue about what you’re really buying.
Understand SOH, DOD, and EOL, and you’ll avoid surprises, downtime, and wasted money.
✅ Always compare like-for-like.
✅ Always get the full test report.
✅ Always plan for real conditions — not just lab numbers!
