What Is mAh in Power Banks?
mAh (milliampere-hour) measures a power bank’s energy storage capacity, like a water tank’s gallon count. A 10,000mAh bank stores enough energy to theoretically charge a 3,279mAh smartphone three times, but real-world efficiency drops this to ~2 charges due to voltage conversion losses (EnergyStar 2022).
Standard smartphone batteries range from 2,500–5,000mAh (Apple/Android spec sheets), while power banks typically offer 5,000–27,000mAh. The higher the mAh, the more energy the bank can deliver—but also the heavier and slower to recharge. For context:
- 5,000mAh: ~1 smartphone charge (ideal for minimalist carry)
- 10,000mAh: 2–3 charges (daily use sweet spot)
- 20,000mAh+: 4–6 charges (travel/multi-device)
Key factors affecting usable capacity:
- Voltage conversion: Power banks output 5V via USB, but store energy at 3.7V—losing ~20% in conversion (IEEE 2021).
- Heat dissipation: Fast charging generates heat, reducing efficiency by 10–15%.
- Battery aging: Capacity drops to 80% after 300–500 full cycles (Battery University).
For deeper capacity insights, see our power bank capacity guide.
How to Calculate Power Bank Charges for Your Device?
Divide your power bank’s mAh by your device’s battery capacity, then multiply by 0.6 for real-world efficiency. A 20,000mAh bank delivers ~12,000mAh usable power (60% efficiency, UL certification), charging a 3,279mAh iPhone ~3.6 times.
Example calculation table:
| Device | Battery (mAh) | Charges from 10,000mAh | Charges from 20,000mAh |
| -------- | -------------- | ----------------------- | ----------------------- |
| iPhone 14 | 3,279 | ~1.8 | ~3.6 |
| Samsung Galaxy S23 | 3,900 | ~1.5 | ~3.0 |
| iPad Air | 7,729 | ~0.8 | ~1.6 |
Critical notes:
- Fast charging reduces efficiency: Quick Charge 3.0 loses ~15% more energy than standard 5V/2A charging (Anker lab tests).
- Multi-device charging: Simultaneous charging splits output, extending total recharge time.
For personalized recommendations, use our power bank selector tool.
Which Is Better: 10,000mAh or 20,000mAh Power Bank?
Choose 10,000mAh for portability (200g) or 20,000mAh for maximum charges (400g, 4–6 devices). A 20,000mAh bank weighs 2x more but delivers 2x the usable charges (Anker PowerCore specs).
Trade-off breakdown:
| Metric | 10,000mAh | 20,000mAh |
| -------- | ----------- | ----------- |
| Weight | ~200g | ~400g |
| Pocket-friendly | Yes | No (requires bag) |
| Charges iPhone 14 | ~2 | ~4 |
| Recharge time (5V/2A) | 6 hours | 12 hours |
| TSA approval | Always | Always (under 100Wh) |
Best use cases:
- 10K: Daily commuters needing 1–2 extra charges
- 20K: Travelers or users with multiple devices (phones + tablets)
Explore high-capacity options for multi-device scenarios.
Should I Get a 10,000mAh or 20,000mAh Power Bank?
Get 10,000mAh for everyday carry or 20,000mAh for travel—TSA allows power banks ≤100Wh (27,000mAh at 3.7V) without approval (FAA 2023). Most users find 10K sufficient: it fits in pockets and charges most smartphones twice.
Decision checklist:
- Daily needs: 10K if you only need backup power for your phone
- Travel: 20K if charging tablets/laptops or going off-grid
- Weight tolerance: 20K models weigh ~400g vs. 10K’s 200g
- Recharge patience: 20K takes 8+ hours to refill from empty
Exception: Laptop users need 20K+ with Power Delivery (e.g., MacBook Air requires 30W PD). See our travel power bank rules for airline specifics.
Why Doesn’t My Power Bank Deliver Its Full mAh?
Power banks lose ~40% of rated capacity due to voltage conversion (5V USB → 3.7V battery) and heat dissipation. A 10,000mAh bank typically delivers ~6,000mAh usable power (60% efficiency, UL testing).
Four hidden drains:
- Conversion loss: 20–25% energy lost stepping voltage up/down
- Cable resistance: Poor-quality cables waste 5–10% power (USB-IF compliance tests)
- Temperature: Below 0°C/32°F, capacity drops 30% temporarily
- Battery wear: After 300 cycles, capacity declines to 80% (Battery University)
Maximize efficiency by:
- Using short, thick USB-C cables
- Avoiding fast charging when not urgent
- Storing at room temperature
Learn maintenance tips in our power bank care guide.
How Does Voltage Affect Power Bank Capacity?
Voltage determines actual energy (Wh), not just capacity (mAh)—calculate Wh as mAh × V ÷ 1,000. USB-C Power Delivery uses 9V/12V for faster charging, while standard USB-A operates at 5V (USB-IF compliance docs).
Key voltage scenarios:
- 3.7V (battery voltage): The stored energy level before conversion
- 5V (USB standard): Output voltage with ~20% conversion loss
- 9V/12V/15V (PD): High-voltage modes for fast charging laptops
Example: A 20,000mAh bank at 3.7V = 74Wh (under TSA’s 100Wh limit). Same capacity at 5V = 100Wh—requiring airline approval.
For fast-charging specifics, visit our fast charging guide.
Bottom Line: How Much mAh Do You Really Need?
Match power bank capacity to your device needs and portability priorities:
- Smartphones: 10,000mAh (2–3 charges, 200g)
- Tablets/laptops: 20,000mAh+ (check device Wh requirements)
- Travel: ≤27,000mAh (100Wh TSA limit)
Pro tips:
- Always derate mAh by 40% for real-world usage
- For laptops, prioritize Power Delivery (PD) over mAh alone
- Weights scale linearly—10K=200g, 20K=400g, 27K=500g
Find your perfect match in our smartphone power bank collection.
