What grade are the cells inside the battery?

A 51.2V LiFePO4 battery may look similar from the outside, but the quality and consistency of the cells inside can have a significant impact on battery performance, reliability, cycle life, and safety.

This is why professional battery manufacturers and system integrators perform rigorous cell classification before cells are assembled into battery packs.

What Does “Cell Grade” Actually Mean?

Cell grading is not simply a matter of labeling cells as “good” or “bad.”

Professional cell classification evaluates multiple parameters, including:

• Open-circuit voltage (OCV)
• Voltage consistency
• Internal resistance
• Actual capacity
• Self-discharge characteristics
• Physical appearance
• Terminal condition
• Sealing quality

These parameters help determine whether a cell is suitable for high-performance battery applications.

For example, the cell classification standard shown in the manufacturing document we reviewed uses different criteria to distinguish A1, A2, H, K and other categories.

A1 Grade: The Highest Consistency Standard

In the referenced classification standard, A1 cells must simultaneously meet five key electrical requirements, including voltage, voltage-change rate, terminal voltage, internal resistance and capacity.

For Gotion 15Ah cylindrical cell specification shown in the document, the A1 criteria include:

• OCV voltage: approximately 3020–3090 mV
• Voltage change rate: ≤3 mV/day
• Terminal voltage: ≥1500 mV
• Internal resistance: approximately 1.0–2.6 mΩ
• Capacity: approximately 15,000–16,200 mAh

The cells must also meet the manufacturer's outgoing inspection requirements for appearance.

The important point is not simply the individual numbers.

It is the combination of multiple parameters.

A cell with good capacity but unusually high internal resistance, for example, may not be equivalent to a cell that performs well across all parameters.

A2 Grade: Qualified Cells With Different Performance Windows

A2 cells also meet defined quality requirements, but their acceptable performance ranges differ from A1 cells.

In the referenced standard, A2 cells have a wider voltage window and different voltage-change and terminal-voltage requirements, while the remaining requirements follow the A1 criteria.

This illustrates an important concept:

Cell grading is about consistency and specification—not simply whether a cell can work.

A cell can be functional while still not meeting the tighter criteria required for the highest grade.

B Grade: Why “B Grade” Is Not One Single Category

Another common misunderstanding is that all B-grade cells are the same.

They are not.

The referenced standard further separates B-grade cells into categories such as H-grade and K-grade, based on different conditions.

For example, H-grade classification can be triggered when a cell does not meet the A1/A2 requirements but meets one or more defined conditions, such as:

• Capacity below the A-grade range
• Platform voltage below the specified threshold
• Internal resistance outside the specified range
• Voltage below the specified limit

K-grade, meanwhile, includes cells identified as having sealing-related defects.

This is why simply asking:

“Are these A-grade cells?”

is not always enough.

A professional buyer should also ask:

What is the grading standard?

What are the actual electrical parameters?

How are the cells tested and sorted?

Cell Consistency Is Just as Important as Capacity

Imagine two cells:

Cell A

15.5Ah
2.0mΩ internal resistance
Stable voltage

Cell B

15.5Ah
3.5mΩ internal resistance
Higher voltage variation

On paper, both cells have almost the same capacity.

But they may behave very differently when assembled into a battery pack.

Different internal resistance and voltage characteristics can lead to differences in:

• Charge and discharge behavior
• Heat generation
• Balancing requirements
• Available power
• Pack consistency
• Long-term aging

This is why capacity alone cannot define cell quality.

Why Cell Matching Matters in a Battery Pack

A battery pack is not simply a collection of individual cells.

It is a system.

When cells are connected in series and parallel, their differences can accumulate.

For example, a 16-cell LiFePO4 battery pack requires the cells to work together as a balanced system.

If one cell has significantly different characteristics from the others, it can become a limiting factor for the entire pack.

Therefore, professional battery production typically involves:

Cell testing

↓

Cell grading

↓

Cell matching

↓

Module assembly

↓

BMS integration

↓

Pack testing

↓

Final quality inspection

The quality of the finished battery begins long before the battery enclosure is assembled.

What Happens to Cells That Fail the Criteria?

Professional classification systems also define cells that should not enter normal battery production.

The referenced document identifies examples of scrap conditions including:

• Electrolyte leakage
• Severe deformation
• Missing steel ball
• Terminal detachment

These are treated as scrap products rather than normal production cells.

This is an important distinction.

A professional battery supply chain should have clear boundaries between:

Qualified cells → downgraded cells → scrap cells

rather than mixing cells of different quality levels without traceability.

Don't Just Ask “A Grade or B Grade”

When buying lithium batteries, we recommend asking suppliers more detailed questions.

Instead of simply asking:

“Are you using A-grade cells?”

Ask:

1. Who manufactured the cells?

2. What is the exact cell model?

3. What is the nominal capacity?

4. What is the typical internal resistance?

5. What are the OCV requirements?

6. How are the cells matched?

7. Is there a cell test report?

8. Is there batch traceability?

9. What is the incoming inspection process?

10. What quality standard is used for grading?

These questions provide much more information than the words “A Grade” alone.

From Cell Quality to Battery Quality

At Wiren, we believe a battery should not be judged by its label alone.

A reliable battery requires a combination of:

Quality Cells

Cell Matching

Reliable BMS

Robust Mechanical Design

Thermal Management

Production Quality Control

Final System Testing

That is the foundation of a dependable energy storage system.

Because ultimately, battery quality is not created by one component—it is created by consistency throughout the entire system.