Expect about 80–85 Wh usable from a 30,000 mAh bank—roughly 4–6 phone charges or 1–2 tablet charges, depending on draw and ports.
A big-capacity pack looks like endless energy, yet the real answer depends on energy in watt-hours (Wh), conversion losses, and what you plug in. Below, you’ll see the quick math, realistic charge counts, and the factors that stretch or shrink runtime.
How Long A 30,000 mAh Power Bank Can Run: Quick Math
Most packs use lithium-ion cells with a nominal 3.7–3.85 V. Energy equals capacity times voltage. A 30,000 mAh pack at 3.7 V holds about 111 Wh (30,000 × 3.7 ÷ 1000). Converters and cables waste some of that, so real usable energy lands near 70–80% for many setups. Using a middle-ground 75% efficiency, you get about 83 Wh delivered to your devices.
What That Means In Plain Terms
- Phones with 12–20 Wh batteries: plan on about 4–6 full charges.
- Small tablets around 28–40 Wh: plan on 1–2 full charges.
- Ultrabooks with 50–60 Wh packs: near a full top-up in the best case.
Broad Charge Estimates (Using ~75% Efficiency)
The numbers below use typical battery sizes many devices ship with and assume you’re charging one device at a time at moderate speed.
| Device Type | Typical Battery (Wh) | Expected Full Charges |
|---|---|---|
| Compact Phone | 12–14 | 6–7 |
| Large Phone | 16–20 | 4–5 |
| Small Tablet / E-Reader | 20–30 | 2–4 |
| 10-Inch Tablet | 28–40 | 1–2 |
| Handheld Game Console | 14–18 | 4–5 |
| Action Camera | 3–5 | 16–25 |
| Mirrorless Camera Battery | 12–16 | 5–6 |
| Earbuds Case | 1–2 | 40–80 |
| Smartwatch | 0.3–0.6 | 130–270 |
| Ultrabook | 50–60 | ~1 |
The Core Formula You’ll Use
Energy math is simple and handy. The relationship is Wh = mAh × V ÷ 1000. A pack rated 30,000 mAh at 3.7 V equals about 111 Wh. A large phone rated 5,000 mAh at 3.85 V equals ~19.25 Wh. Divide usable pack energy by device energy to estimate full charges. If you want a reference for the conversion itself, see a plain-English walkthrough under Wh = mAh × V ÷ 1000.
Worked Example: Big Phone
- Pack energy (nominal): 111 Wh.
- Usable energy after losses (≈75%): ~83 Wh.
- Phone energy: 5,000 mAh × 3.85 V ÷ 1000 ≈ 19.25 Wh.
- Estimated full charges: 83 ÷ 19.25 ≈ 4.3 cycles.
Why Your Result Can Swing Up Or Down
- Conversion losses: Step-up from cell voltage to 5–20 V costs energy.
- Cable and connector loss: Thin, long, or poor-quality leads waste watts as heat.
- Charging speed: Faster ports raise heat, which trims efficiency.
- Device on vs off: If the device is streaming or gaming while charging, your pack also feeds the workload.
- Dual-port output: Split power raises current and heat, which can shave total delivered energy.
- Cold or hot weather: Cells prefer mild temperatures; extremes sap capacity.
Port Specs, Wattage And Real Runtime
Labels list mAh, but your devices drink watts. A USB-C port rated for 30 W pushes double the energy of a 15 W port in the same time. If the bank carries 83 Wh usable, you can estimate how long it can supply a steady load:
| Output Power | Typical Use | Run Time From ~83 Wh |
|---|---|---|
| 10 W | Slow phone/top-off | ~8.3 hours |
| 18 W | Fast phone / small tablet | ~4.6 hours |
| 30 W | Tablet / low-draw laptop | ~2.8 hours |
| 45 W | Ultrabook sipping power | ~1.8 hours |
| 60–65 W | Work laptop while browsing | ~1.2–1.4 hours |
Estimating Charges For Your Exact Device
Step 1: Find Your Device’s Watt-Hours
Check the spec sheet or battery label. Many phones list 3.85 V and a capacity in mAh. Multiply and divide by 1000 to get Wh.
Step 2: Pick An Efficiency Range
Start with 70–80% for day-to-day use. If you push high wattage or chain multiple ports, lean toward the lower end.
Step 3: Divide Usable Pack Energy By Device Energy
Use 83 Wh as a round number for a healthy, mid-efficiency result from a 30,000 mAh pack. That gives quick “about right” answers without a calculator.
Phones, Tablets, And Laptops: What To Expect
Phones
Modern handsets live in the 12–20 Wh band. Many ship with ~5,000 mAh cells at 3.85 V, which sits near 19 Wh. With ~83 Wh on tap, you’ll see four solid full charges, maybe five, assuming you charge while idle and use a sensible cable.
Tablets And Handhelds
Small tablets start near 20–30 Wh; 10-inch models often fall between 28 and 40 Wh. That turns into one to two charges. Handheld consoles resemble large phones in total energy, so counts look similar to the “Phones” row.
Laptops
Thin-and-light machines often sit near 50–60 Wh. If your bank can push 45–65 W over USB-C, you can squeeze in close to a full refill, give or take background load and screen brightness. Heavier notebooks with 70–99 Wh packs need more than one bank or a wall socket for a full cycle.
What Shrinks Or Stretches Runtime
Charging Speed And Heat
Fast ports save time but lose a bit of efficiency. When you’re racing, accept a small drop in total delivered energy. When you care about every last watt-hour, a mid-speed port is friendlier.
Cables And Adapters
Short, quality USB-C to USB-C cables waste fewer watts than long, thin leads or stacks of adapters. Replace worn connectors; extra resistance shows up as heat and lost runtime.
Device Behavior During Charging
Streaming video, mobile gaming, and hotspot duty pull steady power while the battery fills. That turns a “charge count” into “charge while using,” which always reduces the final tally.
Ambient Temperature
Packs deliver best near room temperature. Cold slows chemical reactions; heat raises resistance. Store the bank about half full if it will sit for a month or two.
A Quick Word On Travel Rules
Airlines care about watt-hours, not mAh. Many carriers allow up to 100 Wh in carry-on without approval; 101–160 Wh usually needs airline permission, and checked baggage bans loose power banks. For details, see the current IATA guidance for lithium batteries. A 30,000 mAh pack at 3.7 V is about 111 Wh, which lands in the “ask first” bracket on many routes.
Practical Tips To Get More From Each Charge
Charge Smart
- Use the USB-C PD port when your device supports it; match the label on the bank to your device’s rated draw.
- Top up your phone near 20–60% instead of running it flat; charging is a bit gentler and quicker in that window.
- Turn off the screen or switch to airplane mode during long top-ups on the go.
Keep Losses Low
- Pick short, sturdy cables; avoid daisy-chained adapters.
- Keep the bank and device near room temperature during heavy charging.
- If you need two ports at once, expect a small hit in total delivered energy.
Store And Maintain The Pack
- For long breaks, leave the bank near half charge and in a cool, dry drawer.
- Cycle it every few months to keep the fuel gauge aligned.
- Retire swollen or damaged packs; safety comes first.
Worked Scenarios You Can Copy
Scenario 1: Phone Road Trip
You start with a phone near 15% and plug into a 30 W USB-C port. You stream audio with the screen off and navigate. Expect 4–5 complete refills across a weekend before the bank taps out, since the device draws a little while it fills.
Scenario 2: Tablet On A Flight
A 30 Wh tablet playing offline video on low brightness nets about two full refills. If you switch to a 10 W port and watch while charging, your total delivered energy rises a bit, but the tablet drains part of that on playback.
Scenario 3: Ultrabook At A Cafe
With a 56 Wh laptop and a 65 W PD port, you can push a near-full top-up while working lightly. If the CPU spikes or the screen sits at max brightness, expect a smaller uplift.
How To Sanity-Check A Product Page
Look For Watt-Hours On The Label
Good listings print both mAh and Wh. Wh tells the real story and lines up with travel rules. If Wh is missing, multiply mAh by 3.7 and divide by 1000 for a rough idea.
Check PD Ratings And Port Mix
For laptops, seek USB-C PD at 45–65 W or more. For phones, 18–30 W is plenty. If only one port delivers the big watts, plan your split charging around that.
Weigh The Size Against Your Needs
A 20,000 mAh bank is lighter and still covers a day or two for a phone-heavy user. Pick 30,000 mAh when you want multi-day phone top-ups, a tablet refill, or a laptop assist.
The Bottom Line On Runtime
Think in watt-hours, then apply a realistic efficiency band. From a 30,000 mAh pack, budget ~83 Wh delivered in normal use. That nets 4–6 phone charges, 1–2 tablet charges, or a healthy bump for an ultrabook. Tweak your setup with better cables and sensible port choices, and you’ll squeeze the most from every outing.