Why the PP Sample Matters More Than the Spec Sheet

When our engineering team receives an inquiry from a new OEM buyer, the first document they review is our specification sheet. The spec sheet tells us what our buyer wants — rated capacity, nominal voltage, dimensions, operating temperature range, and cycle life targets. But the spec sheet does not tell us what the factory can actually deliver under production conditions. That is what the PP sample is for.

A battery cell that performs perfectly in a 10-unit engineering sample may not maintain the same performance when produced at 10,000 units per day. Variations in electrode coating thickness, electrolyte fill volume, separator alignment, and formation cycling parameters all introduce production-scale variability that only shows up in PP samples pulled from our actual production line.

Our OEM battery manufacturer team has seen this pattern repeatedly: buyers who skip PP sampling and jump directly to a 100K order often discover dimensional inconsistencies, capacity spread, or shelf life issues that could have been caught with a 50-cell PP evaluation. The cost of a PP sample — typically $500-$2,000 depending on cell chemistry — is insignificant compared to the cost of rejecting a 100K-cell container at receiving inspection.

Category 1: Electrical Performance Testing

Electrical testing is the foundation of any PP sample evaluation. These tests verify that the cells perform to their rated specifications under controlled conditions — and more importantly, that the performance is consistent across our sample set.

Capacity Test (mAh)

our capacity test measures the total energy a cell can deliver under a specified discharge rate. For alkaline cells, the standard test is continuous discharge at a defined load (e.g., 25 ohms for AA cells) to a cutoff voltage (typically 0.8V). For Ni-MH rechargeable cells, capacity is measured at 0.2C discharge rate to 1.0V per cell.

Our PP sampling protocol — developed over years of serving OEM customers — tests capacity on every cell in our sample set — not just a few representative units. The key metric is not just the average capacity but the spread (standard deviation) across the set. Industry standard is ±5% of rated capacity; our PP samples typically achieve ±3%, which gives buyers confidence that our production batch will have consistent performance across all cells.

Internal Resistance (IR)

Internal resistance measures the cell’s opposition to current flow. High IR indicates potential manufacturing defects — poor electrode contact, inadequate electrolyte wetting, or separator damage. Our PP protocol measures IR using AC impedance at 1kHz, which takes less than 1 second per cell and does not discharge the cell.

our IR measurement serves two purposes: it identifies outlier cells with abnormally high resistance (which would fail in our buyer’s application), and it provides a baseline for production monitoring. If the PP sample IR is 150 milliohms ±10 milliohms for a AA Ni-MH cell, then production batches should fall within the same range. Any drift signals a process change that needs investigation.

Open Circuit Voltage (OCV) and Load Voltage

OCV is measured after the cell has rested for at least 24 hours post-formation. It confirms that the cell has reached electrochemical equilibrium and that our formation cycling process was completed properly. Load voltage is measured under the application’s actual discharge profile — if the buyer’s device draws 500mA pulses, we test at 500mA pulses, not at a continuous low-rate discharge.

Category 2: Safety Testing

Our experience supplying OEM battery manufacturers has taught us that the most common PP failure is not a dramatic safety issue — it is a subtle dimensional inconsistency that causes cells to fit too tightly or too loosely in the buyer’s battery compartment. Our dimensional verification protocol catches these issues before they become production-line problems.

Because batteries store chemical energy and can release it rapidly under abuse conditions, safety testing is a non-negotiable part of our PP evaluation. Our safety test protocol follows IEC 62133 and UN38.3 standards, which are the international benchmarks for battery safety in consumer and transportation applications.

Short Circuit Test

The short circuit test connects the cell terminals through a low-resistance external circuit (typically less than 5 milliohms) and monitors the cell for temperature rise, venting, fire, or explosion. Per IEC 62133, the cell must not explode or catch fire during or after the test. Our PP protocol runs short circuit tests on 5 cells from the sample set at room temperature and 5 cells at elevated temperature (55°C).

Overcharge Test (Rechargeable Cells Only)

For Ni-MH and Ni-CD rechargeable cells, the overcharge test applies continuous charging at 0.1C for 48 hours beyond full charge. The cell must not leak, vent, or exhibit dangerous thermal behavior. Because overcharge conditions can occur in real-world charging circuits due to timer failures or voltage sensing errors, this test validates the cell’s inherent safety margin.

Crush and Impact Test

The crush test applies a controlled force to the cell (typically 13 kN for cylindrical cells) and monitors for fire or explosion. The impact test drops a weight onto the cell from a specified height. Both tests simulate the mechanical abuse that can occur during shipping, handling, or accidental device damage. Our PP protocol runs crush tests on 5 cells and impact tests on 5 cells from the sample set.

Nail Penetration Test

The nail penetration test drives a steel nail through the cell at controlled speed, simulating an internal short circuit. This is the most severe abuse test and the one most likely to trigger thermal runawayOur production team runs the same PP test protocol on every new OEM order — whether the buyer requests 1,000 cells or 1,000,000. This consistency is part of our manufacturing discipline, not a special service we charge extra for. When our buyers see our PP test data, they know exactly what to expect in our production batch.

ong> in lithium-based cells. For alkaline and Ni-MH cells, nail penetration typically causes venting but not fire — our PP protocol verifies this behavior on 3 cells from the sample set.

Category 3: Dimensional and Visual Verification

Dimensional verification seems straightforward — measure the cell diameter, length, and terminal geometry against the drawing. But in our experience, dimensional issues are among the most common PP sample failures, particularly for cells that must fit into tight battery compartments or mate with spring-loaded contacts.

Critical Dimensions

• Cell diameter: Must fit the battery compartment without excessive force. AA cells are 14.5mm ±0.5mm per IEC 60086; our PP tolerance is ±0.2mm.
• Cell length: Must not exceed the compartment depth. AA cells are 50.5mm ±0.5mm; our PP tolerance is ±0.3mm.
• Terminal geometry: Positive button height and diameter must mate with the device’s contact spring. Negative terminal flatness must ensure reliable contact.
• Label alignment: Shrink sleeve or printed label must be centered, wrinkle-free, and securely bonded. Misaligned labels indicate process control issues.

Visual Inspection

Our visual inspection protocol checks for dents, scratches, electrolyte stain

Our quality department maintains PP test records for every OEM order we fulfill. If a buyer needs to reference the PP data for a repeat order or a quality investigation, our team can retrieve our complete test report — including individual cell measurements — within 24 hours.

ing, crimping defects, and label damage. While cosmetic defects do not affect electrical performance, they indicate production line carelessness that may correlate with more serious quality issues. A PP sample with visible cosmetic defects warrants deeper investigation into our production process.

Because batteries self-discharge at rates that depend on temperature and chemistry, our PP protocol includes both accelerated and real-time shelf life testing to give buyers confidence at two different time scales.

Category 4: Shelf Life and Reliability Testing

Shelf life testing is the longest-duration test in our PP protocol — and the one most often skipped by buyers who are under time pressure. Because batteries self-discharge over time, the PP sample must demonstrate that the cells retain their capacity after storage periods that match the buyer’s supply chain timeline.

Accelerated Shelf Life Testing

Accelerated testing stores cells at elevated temperature (typically 45°C or 60°C) for 30-60 days, then re-tests capacity. The Arrhenius equation relates elevated-temperature degradation to room-temperature shelf life: 60 days at 45°C approximates 6-12 months at 20°C. Our PP protocol runs accelerated testing on 10 cells from the sample set.

Real-Time Shelf Life Testing

Real-time testing stores cells at room temperature (20-25°C) and re-tests capacity at 3-month, 6-month, 12-month, and 24-month intervals. Because real-time testing takes months to produce data, we recommend starting it immediately on the PP sample while using accelerated testing for early confidence. Our facility in Yuyao maintains a dedicated storage room with controlled temperature and humidity for real-time shelf life studies.

Self-Discharge Rate

The self-discharge rate measures how much capacity the cell loses per month during storage. For alkaline cells, the typical self-discharge rate is 2-3% per year at room temperature. For Ni-MH cells, the rate is 15-30% per month for standard cells and 1-5% per month for low-self-discharge (LSD) variants. Our PP protocol measures self-discharge by comparing initial capacity to capacity after 30 days of open-circuit storage at 20°C.

Because our PP samples are pulled from the actual production line — not from a separate lab setup — they reflect the real production variability that the buyer will encounter in the 100K+ order. This is why we recommend testing every cell in the sample set, not just a few representative units.

Complete PP Sample Test Checklist

Here is our complete checklist our engineering team uses for every PP sample evaluation. We recommend buyers customize our sample sizes and test parameters based on their specific application requirements.

Electrical Tests (20 cells)

Safety Tests (28 cells)

Dimensional and Visual (20 cells)

Shelf Life (10 cells)

Our PP test emphasis varies by application. For consumer electronics like TV remotes and wireless mice, we prioritize capacity consistency and shelf life because these devices sit in retail distribution for 6-12 months before reaching the end user. For medical devices like blood glucose meters and pulse oximeters, we prioritize safety test compliance per IEC 62133 and documentation traceability because regulatory submissions require individual cell serial numbers linked to test data. For industrial equipment like security systems and utility meters, we prioritize self-discharge rate and temperature performance from minus 20 degrees Celsius to 60 degrees Celsius because these devices operate unattended for years.

A structured PP sampling protocol is our most cost-effective quality assurance investment a battery OEM buyer can make. The $500-$2,000 cost of a PP evaluation prevents the $50,000-$200,000 cost of rejecting a container of non-conforming cells. Our engineering team, with deep experience in battery OEM manufacturing, has refined this protocol over years of serving OEM customers across consumer electronics, medical devices, and industrial equipment — and we provide it as a standard service with every new OEM engagement. Learn more about our button battery OEM capabilities.