Power Bank Specs for OEM Buyers: mAh, Capacity & Performance Guide
QUICK ANSWER
What does mAh mean? mAh stands for milliampere-hours — it measures how much electrical charge a battery can store. A 10,000mAh power bank can theoretically deliver 10,000mA (10 amps) for one hour, or 1,000mA for 10 hours. But the rated number is NOT what your phone receives — due to the 3.7V→5V voltage conversion, usable capacity = 60-92% depending on cell grade and circuit quality. When evaluating OEM factories, demand: (1) Grade-A cells with ≥85% efficiency, (2) actual capacity test reports, (3) 100% aging test. Formula: Usable mAh = (Rated mAh × 3.7V × 0.85) ÷ 5V.
Table of Contents
1. mAh Fundamentals for OEM Buyers: What Battery Cell Specifications Actually Mean
For OEM buyers evaluating battery cells, mAh is the primary specification on every supplier datasheet — and the one most frequently misrepresented. A milliampere-hour (mAh) is a unit of electric charge. It tells you how much current a battery can supply over time:
- 1,000 mAh = can deliver 1,000mA (1 amp) for 1 hour
- 10,000 mAh = can deliver 10,000mA for 1 hour, OR 1,000mA for 10 hours
- 20,000 mAh = can deliver 20,000mA for 1 hour, OR 1,000mA for 20 hours
mAh (milliampere-hours) is the most frequently misrepresented specification on OEM supplier datasheets. At the cell level (3.7V nominal), mAh describes total stored energy. However, after 5V USB boost conversion and PCB efficiency losses, actual usable output is typically 60-70% of the rated cell capacity. For OEM buyers, the critical verification step is measuring actual 5V output mAh — not trusting the cell label.
The "milli" prefix means one-thousandth. 1,000 milliamps = 1 amp. So a 10,000mAh battery stores the same charge as a 10Ah (amp-hour) battery. The mAh unit is used because it produces friendlier numbers for consumer electronics — "10,000mAh" reads better than "10Ah" on a product box.
2. Grade-A Cells & OEM QC: Rated vs Usable Capacity
This is the single most important thing to understand about power bank specifications — and the one manufacturers don't advertise prominently.
The 3.7V → 5V Problem
Lithium-ion and lithium-polymer cells operate at a nominal voltage of 3.7V. This is the voltage at which mAh capacity is measured and advertised. But USB output requires 5V (or higher — 9V, 15V, 20V for fast charging). To bridge this gap, every power bank contains a boost converter circuit that steps up the voltage. This conversion is not free — it costs 15-35% of the stored energy, lost as heat.
At 3.7V: 10,000mAh × 3.7V = 37 watt-hours (Wh) of stored energy
At 5V output: the same 37Wh ÷ 5V = 7,400mAh theoretical maximum
After efficiency losses (~85%): 7,400 × 0.85 = ~6,290mAh actually delivered
Efficiency Varies by Quality
| Power Bank Tier | Conversion Efficiency | 10,000mAh → Usable |
|---|---|---|
| Premium (GaN, quality components) | 88-92% | ~6,500-6,800mAh |
| Mid-range (standard quality) | 75-85% | ~5,500-6,300mAh |
| Budget / No-name | 60-70% | ~4,400-5,200mAh |
This is why two "10,000mAh" power banks can deliver noticeably different real-world performance. The efficiency of the boost converter circuit and the quality of the battery cells matter enormously.
WOWOHCOOL Factory Data: Branded Cell Capacity Verification (10,000mAh Rated Cells, 10-Unit Sample per Brand)
| Cell Brand / Model | Rated mAh | Measured @ 5V/2A | Conversion Eff. | Deviation |
|---|---|---|---|---|
| Samsung SDI INR18650-35E | 3,500mAh | 6,520mAh | 91.5% | −1.2% vs rated |
| LG M50T 21700 | 5,000mAh | 6,480mAh | 91.0% | −1.5% vs rated |
| ATL Li-Polymer 604068 | 5,000mAh | 6,310mAh | 88.6% | −2.8% vs rated |
| Bak 18650 N18650CP | 2,600mAh | 5,870mAh | 82.4% | −5.1% vs rated |
| Generic "Grade-A" (unnamed) | 5,000mAh claimed | 4,820mAh | 67.7% | −15.3% vs claimed |
All cells configured as 2× series (7.4V nominal) in 10,000mAh-rated power bank PCB. Measured at 5V/2A USB output using Chroma 63600 DC load. 10-unit sample per brand, values are batch averages. The "Generic" row represents an unnamed cell sourced from a non-certified supplier — typical of budget power banks claiming Grade-A status. This is why WOWOHCOOL exclusively sources cells from Samsung SDI, LG Energy Solution, and ATL with batch-level certification documentation.
3. OEM Conversion Formula: Calculating Usable Capacity for Product Spec Sheets
THE FORMULA
Usable mAh = (Rated mAh × 3.7V × Efficiency) ÷ Output Voltage
For standard 5V USB output with 85% efficiency:
Usable mAh = Rated mAh × 0.629
Example 1: 5,000mAh Bank
(5,000 × 3.7 × 0.85) ÷ 5 = ~3,145mAh usable — about 1 full iPhone charge
Example 2: 10,000mAh Bank
(10,000 × 3.7 × 0.85) ÷ 5 = ~6,290mAh usable — about 1.5-2 iPhone charges
Example 3: 20,000mAh Bank
(20,000 × 3.7 × 0.85) ÷ 5 = ~12,580mAh usable — about 3-4 iPhone charges
4. mAh vs Wh for OEM Compliance: Air Freight Limits & Product Labeling Requirements
Watt-hours (Wh) is the more honest unit for comparing battery capacity because it accounts for voltage differences. Here's why:
mAh (Milliampere-Hours)
Pros: Familiar, easy to compare within the same voltage category
Cons: Misleading when comparing devices with different voltages. A 5,000mAh laptop battery at 11.4V stores 57Wh — more energy than a 10,000mAh power bank at 3.7V (37Wh). mAh alone doesn't tell the full story.
Wh (Watt-Hours)
Pros: Voltage-independent — directly compares total energy regardless of battery chemistry or device type
Cons: Less familiar to consumers. Used by airlines for safety regulations (100Wh carry-on limit).
mAh → Wh Conversion
Wh = (mAh × Voltage) ÷ 1,000
10,000mAh @ 3.7V = 37Wh · 20,000mAh @ 3.7V = 74Wh · 27,000mAh @ 3.7V = 99.9Wh (airline limit)
5. End-User Charge Estimates by Capacity Tier: What to Print on Retail Packaging
| Power Bank | iPhone 16 (~3,300mAh) | Galaxy S25 (5,000mAh) | Pixel 9 Pro (~4,700mAh) | iPad Air (~7,500mAh) |
|---|---|---|---|---|
| 5,000mAh | ~0.9 | ~0.6 | ~0.6 | ❌ |
| 10,000mAh ★ | ~1.9 | ~1.3 | ~1.3 | ~0.8 |
| 20,000mAh | ~3.8 | ~2.5 | ~2.7 | ~1.7 |
| 27,000mAh | ~5.1 | ~3.4 | ~3.6 | ~2.3 |
*Assumes 65% overall efficiency (budget to mid-range conversion). Premium GaN power banks will achieve ~10-15% more charges. Real-world results vary with ambient temperature, cable quality, and whether the phone is in use while charging.
6. OEM Cell Sourcing Quality Specs: What to Demand from Your Battery Factory
Spec Verification #1: Capacity Scales Near-Linearly — Demand Batch Test Proof
A 20,000mAh bank should deliver approximately 1.8-2× the usable capacity of a 10,000mAh bank from the same production line. Non-linear results — e.g., 20,000mAh delivering only 1.3× — indicate inconsistent cell quality or circuit efficiency degradation at higher capacities. OEM QC requirement: request batch test data at both the minimum and maximum capacity tiers in your order.
Spec Verification #2: mAh ≠ Speed — Verify Both Capacity AND Wattage on the QC Report
mAh measures stored energy (capacity). Wattage measures delivery rate (speed). A supplier's QC report listing mAh without confirming wattage output at each port is incomplete. A 20,000mAh bank outputting only 10W charges devices slower than a 10,000mAh bank at 30W. OEM QC requirement: the final inspection report must list both rated mAh AND measured wattage output per port at 5V, 9V, 15V, and 20V.
Spec Verification #3: Charge Count Claims Require Conservative Math — Audit Your Supplier's Numbers
The formula every OEM buyer must verify: (Rated mAh × 0.65) ÷ target phone mAh = realistic charge count. A 10,000mAh bank charging a 5,000mAh phone delivers ~1.3 charges at 65% efficiency — not 2.0. To deliver 2 full charges, you need a ~15,400mAh cell. OEM QC requirement: demand your factory calculate charge-cycle estimates using 65% efficiency (the industry-standard conservative baseline) and print that number on retail packaging to preempt capacity-related returns.
More resources: Now that you understand mAh and cell quality verification, read our Power Bank OEM Manufacturer: Custom & Wholesale Sourcing Guide for capacity tier strategy, FOB pricing, and OEM product line planning, or explore Power Bank Specs for OEM Importers for a technical deep-dive into charging protocols and certification requirements.
WOWOHCOOL FACTORY STAT
WOWOHCOOL sources Grade-A lithium-polymer cells exclusively from Samsung SDI, LG Energy Solution, and ATL — verified by batch-level certification and random-sample teardown inspection. Every power bank cell is tested at 5V/2A USB output (not just 3.7V cell voltage) to confirm usable capacity before assembly. GaN-based circuits achieve measured conversion efficiency of 88-92% on Chroma 63600 load testers — verified per production lot. Reject threshold: any cell delivering below 85% of rated usable capacity at 5V output. View our power bank catalog →
Sourcing Power Banks with Accurate Capacity Specs?
WOWOHCOOL publishes both rated and tested usable capacity for every model. Factory-direct OEM/ODM with MOQ from 500 units.
EXPERT INSIGHT
"The number one question we get is 'why does my 10,000mAh power bank only charge my phone 1.5 times?' The answer is physics, not a defect. That 30-40% voltage conversion loss is real and consistent across all brands. The difference between premium and budget isn't rated mAh — it's conversion efficiency. Our GaN-based banks hit 92%, while budget circuits barely reach 65%."
— Nina Nico, OEM Technical Lead at WOWOHCOOL
Supply Chain Expert · Wireless Charging Specialist
Nina Nico is a supply chain management expert with 10+ years experience helping global B2B clients source quality power banks from WOWOHCOOL — a premium charging solution specialist in Shenzhen, China. She holds a degree in International Trade and is a certified supply chain professional (CSCP).