A power bank’s watt output ranges from 5–65W, while some USB-C PD units reach 100–240W; actual draw depends on your device and cable.
Shopping for a portable charger is confusing because boxes shout out milliamp hours, ports, and fast-charge badges. What you really need is clear guidance on watts: how much power a bank can send, how quickly it can recharge your gear, and what to expect in real life. This guide breaks that down with plain numbers, short steps, and two quick tables you can use while buying or setting up your kit.
How Many Watts A Power Bank Delivers In Practice
Most basic units send 5–12 watts through a USB-A port. Popular mid-range models with USB-C Power Delivery (PD) ship in the 18–30 watt band, enough for modern phones and small tablets. Larger USB-C banks step up to 45–65 watts for compact laptops and gaming handhelds, and a handful go to 100 watts or more with the right cable. The ceiling of the standard now reaches 240 watts, but only certain chargers and cables support that level. Your device also sets a cap, so the real number is the lower of the bank’s port rating and your gadget’s charge limit.
Watts Vs. Watt-Hours Vs. Milliamp Hours
Watts (W) describe power or charge speed. Watt-hours (Wh) describe stored energy. Milliamp hours (mAh) is just a battery’s capacity number at its nominal voltage. To compare apples to apples across power banks, convert mAh to Wh:
Watt-hours (Wh) ≈ (mAh × 3.7 V) ÷ 1000
That 20,000 mAh pack holds roughly 74 Wh. If your phone accepts 20 W while fast-charging, that bank could, in a perfect world, power it at full tilt for a bit under four hours of charging time in total. Losses and tapering reduce that figure; plan for ~65–75% of the labeled energy to reach the device, depending on quality, cables, and ambient heat.
What Controls The Number You See
- Port Type: USB-A usually peaks at 10–12 W; USB-C opens the door to 15 W without PD and 18–240 W with PD and the right cable.
- Voltage/Current Profile: 5 V, 9 V, 12 V, 15 V, 20 V are common PD steps; multiply by current (amps) to get watts.
- Device Request: Phones, tablets, and laptops “ask” for power; the bank negotiates a safe level and sticks to it.
- Cable Rating: Some high-wattage modes require an e-marked USB-C cable; weak cables bottleneck the flow.
- Thermal Limits: If the pack heats up, firmware can dial back output to protect the cells.
Common Output Standards And Realistic Watt Levels
The table below lists popular charging modes you’ll see on boxes and spec sheets and the watts they commonly allow.
| Standard / Port | Typical Voltage × Current | Max Watts You’ll See |
|---|---|---|
| USB 2.0 / USB-A | 5 V × 0.5–0.9 A | 2.5–4.5 W |
| USB Battery Charging 1.2 (USB-A) | 5 V × 1.5 A | 7.5 W |
| USB-C Current Mode (non-PD) | 5 V × 3 A | 15 W |
| USB-C Power Delivery (entry) | 9 V × 2 A or 12 V × 1.5 A | 18 W |
| USB-C PD (phones/tablets) | 5–12 V up to 3 A | 20–30 W |
| USB-C PD (ultrabooks/handhelds) | 15–20 V up to 3 A | 45–60 W |
| USB-C PD (high-power) | 20 V × 5 A | 100 W |
| USB-C PD 3.1 (EPR) | Up to 48 V × 5 A | Up to 240 W (charger/cable/device dependent) |
These numbers reflect port capability, not a promise that your phone or laptop will draw the top value. A phone that caps at 27 W won’t pull 60 W, even from a 60 W port.
Quick Way To Read A Label
Flip the bank and scan for lines like “USB-C1: 5V⎓3A, 9V⎓2A, 12V⎓1.5A (18W).” That’s the maximum per port. If you see “Total Output 45W,” the unit might share that pool across ports; plugging in two devices splits the budget. When the spec lists both “Output 65W” and “Input 30W,” it means it can send 65 W to your gear and accept 30 W when you recharge the pack itself.
How Many Watts You Actually Get With Real Devices
Phones
Modern iPhones and Android flagships sit in the 18–30 W band on USB-C PD. Some vendor-specific bricks can show bigger numbers, but cross-brand results tend to land in that 20–30 W range with a PD bank. Expect fast top-ups to taper near 80% state of charge.
Tablets
Small and mid tablets draw 18–30 W. Large pro tablets can ask for 30–45 W, especially during heavy use or while powering a keyboard case.
Ultrabooks And Slim Laptops
Many thin laptops drink 45–65 W over USB-C. If your model ships with a 65 W or 100 W adapter, match or exceed that rating on your bank for steady performance while the machine is under load.
Gaming Handhelds And Accessories
Handheld PCs and docked accessories often sit around 45 W. A 60–65 W bank gives headroom for play while charging.
Estimate Run Time And Charge Time
You can ballpark charge time with two inputs: stored energy and expected watt draw.
- Convert capacity: 10,000 mAh ≈ 37 Wh; 20,000 mAh ≈ 74 Wh; 26,800 mAh ≈ ~99 Wh.
- Factor losses: assume ~70% of Wh reaches the device.
- Divide by draw: usable Wh ÷ watts ≈ hours of full-tilt charging.
Example: a 20,000 mAh bank (~74 Wh) feeding a phone that averages 12 W while charging. Usable energy might be ~52 Wh. 52 Wh ÷ 12 W ≈ ~4.3 hours of charging time spread across sessions. Fast-charge peaks near the start; tapering stretches the last 20%.
How Many Watts The Bank Itself Needs To Recharge
Input wattage sets how fast the pack refills. Small units often accept 10–18 W over USB-C. Mid-size packs take 20–30 W, and bigger models may accept 45 W or 60 W. If your wall charger can send more than the bank’s input rating, the bank still caps to its own limit. Want faster top-offs? Choose a bank with a higher input spec and pair it with a capable USB-C PD wall charger and a proper cable.
Cable And Accessory Checklist
- Use e-marked USB-C cables for any setup beyond 3 A or 60 W.
- Keep cables short for less voltage drop at higher loads.
- Replace worn leads; crushed or loose connectors limit current and can trigger throttling.
Travel Note: Watt-Hour Labels And Flight Rules
Airlines look at watt-hours, not watts. Banks under 100 Wh usually fly in carry-on with no special paperwork. Between 101–160 Wh, many airlines ask for approval and set a two-spare limit; packs above that range often aren’t allowed. Always keep the bank in the cabin, never checked.
For the tech standard behind higher-watt USB-C charging, see the USB Power Delivery overview. For cabin rules, check the FAA’s PackSafe lithium batteries page.
Quick Picker: Match Device To Bank Output
| Device Type | Recommended Port Output | What That Delivers |
|---|---|---|
| Budget/older phones | 10–12 W (USB-A) | Reliable top-ups; not “fast charge” |
| Modern phones | 18–30 W (USB-C PD) | Fast charge to ~50% quickly, then taper |
| Small tablets/ereaders | 18–30 W (USB-C PD) | Steady charging while in use |
| Large tablets | 30–45 W (USB-C PD) | Keeps charging during heavy apps |
| Ultrabooks | 45–65 W (USB-C PD) | Maintains battery while working |
| High-power laptops* | 100–140 W+ (PD 3.1) | Light loads on supported models |
*Many gaming laptops and workstations ship with proprietary adapters; USB-C may charge slowly or only when idle.
Troubleshooting Slow Or Stalled Charging
It Says 30 W But I Only See 12 W
Swap the cable for a known good USB-C lead. Make sure you’re on the bank’s USB-C PD port, not a legacy USB-A port. Check that your device supports PD at the claimed rate. Some phones need a setting toggled for fast charge while the screen is on.
Output Drops After A Few Minutes
That’s charge tapering. As the device battery fills, the current request drops to manage heat and cell safety. You can’t bypass tapering, but you can start from a lower state of charge to see quicker gains in a short window.
Charging Stops When I Plug Two Devices
Many packs share a total watt budget. If the label reads “Total 45 W,” two hungry devices can overload that pool and trigger a reset. Unplug one device, or look for a unit that lists higher “Total Output” and per-port limits.
Buying Tips That Save Headaches
- Start with your device’s max input. If your laptop wants 65 W, pick a bank with a 65 W or 100 W port.
- Pick capacity by use case. Daily carry: 10,000–12,000 mAh. Weekend trips: 20,000 mAh. Laptop days: 25,000–27,000 mAh (near the 100 Wh flight threshold).
- Check input spec. A 30–60 W input refills a big pack much faster than a 10–18 W input.
- Look for clear labeling. Per-port watts, total output, and input watts should be listed on the shell or spec sheet.
- Mind the cable. For anything above 60 W, keep an e-marked USB-C cable in your bag.
Realistic Expectations For High-Watt PD 3.1
PD 3.1 raises the ceiling to 240 W with Extended Power Range. That figure applies to wall chargers and certain cables first, while mobile banks will roll out more slowly due to size, heat, and cell pack constraints. Expect the sweet spot for power banks to remain 45–100 W for some time, which already covers thin laptops and most mobile gear. If you spot a spec above 100 W on a portable unit, check for size, weight, and whether your laptop supports that mode.
The Takeaway
A pocket-size bank sends 5–12 W; a solid mid-sizer with USB-C PD lands at 18–30 W; bigger bricks deliver 45–65 W, with select models reaching 100 W or beyond. Match the bank’s port wattage to your device’s needs, convert mAh to Wh to gauge capacity, and bring the right cable. That’s the entire puzzle of “how many watts” turned into simple, reliable choices.