A 27,000 mAh power bank (~100 Wh) typically gives 4–9 phone refills or 2–5 hours of light laptop use, depending on efficiency and load.
A 27,000 mAh pack sits at the top end of carry-on friendly sizes because its energy is about 100 watt-hours. That’s why travelers like it: plenty of juice, still airline-compliant, and capable of keeping phones, tablets, cameras, and even thin-and-light laptops alive through a long day. The catch is that “how long it lasts” depends on three things—usable watt-hours after conversion losses, the device’s battery size or draw, and how you use it. This guide shows the quick math, gives realistic ranges, and shares easy rules you can trust.
Quick Answer And Why It Varies
Inside most packs are 3.7 V lithium-ion cells. Converting 27,000 mAh at 3.7 V gives about 99.9 Wh. After conversion overhead (heat, voltage step-up, cable loss), you don’t get all of that. Good packs deliver roughly 80–90% of the stored energy to your device. That leaves 80–90 Wh usable in day-to-day charging.
How Long 27,000 mAh Packs Really Run — The Short Math
Use two simple approaches:
- Charging full devices: Usable Wh ÷ device battery Wh ≈ number of full charges.
- Powering devices directly: Usable Wh ÷ device watt draw ≈ hours of runtime.
For a quick example, many phones have 12–18 Wh batteries. With ~85 Wh usable, you’ll see ~4–7 full refills. A thin laptop pulling ~18 W for light work would run ~4–5 hours from the pack alone; bump that draw to ~30 W and you’ll see ~2–3 hours.
Early Snapshot: What You Can Expect
The table below gives a broad, scan-friendly overview using a realistic 85% efficiency (≈85 Wh usable) and common device battery sizes.
| Device | Battery (Wh) | Approx Full Charges* |
|---|---|---|
| Modern Phone (small) | ~12 Wh | ~7 refills |
| Modern Phone (large) | ~17 Wh | ~5 refills |
| Compact Tablet | ~28 Wh | ~3 refills |
| 11–13″ Tablet | ~35 Wh | ~2 refills |
| Mirrorless Camera | ~15 Wh | ~5 refills |
| Wireless Earbuds Case | ~3 Wh | ~28 refills |
*Estimates assume ~85 Wh usable. Real results swing with cable quality, charging speed, and device behavior near 100%.
Why 27,000 mAh Equals About 100 Wh
Watt-hours tell you energy; mAh tell you charge at a given voltage. The standard equation is:
Wh = (mAh ÷ 1000) × V
Most cells inside a pack sit around 3.6–3.7 V nominal. So a 27,000 mAh pack at 3.7 V is roughly 99.9 Wh. That’s the same math used by air-travel regulators and shipping rules. You can see the Watt-hour formula straight from IATA, and the U.S. DOT/PHMSA repeats it in plain terms as Wh = (mAh÷1000) × Volts for lithium-ion batteries. These references also explain why airlines use 100 Wh as a threshold.
Travel Note: The 100 Wh Threshold
A 99–100 Wh pack normally qualifies for passenger carry-on, while spare lithium batteries and power banks must stay out of checked bags. You’ll find this spelled out on the official TSA power bank page and in the IATA passenger guidance. Pack it in your cabin bag, keep ports covered, and avoid storing it where it can get pinched or overheated.
Usable Energy: Why You Never See The Full 100 Wh
USB-C Power Delivery and other fast-charge protocols step voltage up and down. That conversion costs energy. Better electronics waste less, but no pack is loss-free. Expect around 80–90% of the label to reach your device across a day of top-ups. Fast charging at high wattage can shave a little more off due to heat. Cable resistance, pass-through losses, and charging above 80% also reduce end-to-end efficiency.
Realistic Outcomes By Device Type
Phones
Many current phones sit between ~12 and ~18 Wh. With ~85 Wh usable, the range lands near 4–7 complete refills. If you trickle charge while navigating, filming, or gaming, expect fewer full equivalents because part of the energy goes to live use.
Tablets
Compact slates start in the high-20 Wh range; larger models push into the 30s. You’ll usually see ~2–3 complete refills from an all-day pack, with more conservative use when streaming or drawing at full brightness.
Laptops
Runtime depends on watt draw, not battery size, when feeding a laptop directly. Light tasks on efficient machines sip ~15–25 W. Photo work, many tabs, or high brightness can lift that to 25–40 W. Anything pushing a dGPU climbs much higher. Use the runtime formula below to set expectations.
Runtime Formula You Can Use
Hours ≈ Usable Wh ÷ Device W. With an 85 Wh usable budget:
- At 15 W (light typing, dimmer screen): ~5.7 hours
- At 20 W (mixed tasks): ~4.2 hours
- At 30 W (heavier workloads): ~2.8 hours
- At 45 W (sustained loads): ~1.9 hours
If your pack supports fixed-voltage PD profiles (say 20 V at 3 A = 60 W max), match the profile to your laptop’s requirements and expect shorter runtimes at higher draws.
Step-By-Step: Estimating Your Own Runtime
- Convert mAh to Wh: multiply by 3.7 and divide by 1000. Round to ~100 Wh for 27,000 mAh.
- Apply efficiency: multiply by 0.85 for a cautious budget (≈85 Wh).
- Pick a scenario: refills (divide by device battery Wh) or live power (divide by device watts).
- Adjust to reality: subtract 5–15% if you use long, thin cables or keep fast charge pinned at max for hours.
Charging Speed Versus Total Energy
Fast output (e.g., 45–65 W PD) doesn’t add capacity; it just shortens time to charge a device that can accept that speed. If your phone caps at 27 W, a 100 W socket won’t push more once the negotiation settles. Total refills still depend on usable Wh.
Multi-Device Use And Split Ports
Running two ports at once divides the power budget. Many packs share a total output ceiling across ports. When you power a laptop on one port and a phone on another, the controller may throttle both, which stretches charge times and increases conversion loss. If endurance matters more than speed, charge devices one at a time—especially the big ones.
Heat, Cables, And Small Tweaks That Add Hours
- Keep it cool: warm cells waste energy and age faster. Shade the pack and avoid tight pockets near heaters or sun-blasted dashboards.
- Use short, thick cables: lower resistance means less waste. USB-C cables rated for the wattage you need are worth it.
- Turn down peaks: a slightly dimmer screen, lower refresh rate, and closing high-draw apps extend runtime in a big way.
- Top up earlier: cells charge more efficiently from mid levels than from nearly empty to full.
Device Battery Sizes: Handy Reference
Battery capacities for popular phones often land around 13–17 Wh. Independent roundups place recent models in that band, which aligns with manufacturer filings and teardowns. Combine those figures with the runtime math here to forecast your own refills.
Laptop Runtime Scenarios (85 Wh Usable)
These rounded figures assume steady draw while powered by the pack. Real workloads jump around, so treat them as ballpark guides.
| Use Case | Power Draw (W) | Estimated Hours* |
|---|---|---|
| Writing, 40–60% Brightness | ~15–18 W | ~4.7–5.7 h |
| Web + Calls, 70% Brightness | ~20–25 W | ~3.4–4.2 h |
| Photo Edits, Many Tabs | ~30–35 W | ~2.4–2.8 h |
| Code Compile, Light GPU | ~40–50 W | ~1.7–2.1 h |
*Rounded from Hours ≈ 85 Wh ÷ W.
USB-C PD Profiles And What They Mean For You
Most large packs support PD profiles like 5 V, 9 V, 12 V, 15 V, and 20 V with current limits per port (e.g., 20 V × 3 A = 60 W). If your laptop needs 65 W and the pack tops out at 45–60 W, it should still charge at idle or light load, but it may hold level or slowly drain under heavy tasks. For phones, the pack often switches among 9–12 V during fast charge phases, then settles to a lower rate near 80–90% to manage heat. That taper is normal and affects time-to-full more than total refills.
Capacity Labels, Cell Count, And Why Some Packs Outlast Others
Two 27,000 mAh packs can behave differently. Higher-end BMS chips waste less, thicker busbars cut resistance, and better cables keep voltage sag down. Some designs hold output wattage better at low state-of-charge, which avoids mid-charge dropouts on laptops. If endurance is your goal, look for honest Wh labeling, clear PD specs, and published efficiency or conversion charts from the maker.
Practical Examples
Phone-Heavy Day
You shoot clips, post, and navigate between meetings. Your phone battery is ~15 Wh. With ~85 Wh available, plan on around five full equivalents. Shooting 4K and running maps eats power while charging, so expect closer to four in real life.
Tablet On The Road
A mid-size slate at ~30 Wh sees around two full refills. Streaming HDR at max brightness will cut that number; reading or note-taking stretches it.
Light Laptop Work Session
A modern 13″ machine pulling ~18–22 W gets ~4 hours from the pack. If you plug in a phone at the same time, share wisely or you’ll land closer to 3–3.5 hours.
Simple Rules That Make Estimates Stick
- Think in Wh for energy and W for rate. Match them with “hours ≈ Wh ÷ W.”
- Budget 10–20% loss across electronics and cables.
- Fast charge is about time to fill, not total capacity.
- One device at a time gets you the best efficiency.
- Cool pack, short cable, saner brightness = more hours.
Travel Compliance At A Glance
Packs near 100 Wh are designed with air rules in mind: carry-on only, terminals protected, and quantity limits that vary by airline. Official pages back this up with plain language and the same Wh math used here. Skim the TSA lithium battery rule and the IATA passenger guide before you fly.
FAQ-Free Takeaways (No Fluff)
What Most Users See
Phone-centric folks get multiple days of top-ups with room to spare. Mixed phone/tablet users finish a long weekend without hunting for outlets. Thin-and-light laptop users can carve out a few extra working hours between charges, especially with sensible brightness and single-app focus.
When Results Drop
High refresh screens, long 5G hotspots, file exports, and running two devices at once cut endurance. Stashing the pack in a warm pocket, using a long skinny cable, or living at full fast-charge rate also trims your totals.
Wrap-Up You Can Act On
A 27,000 mAh class pack gives you about 80–90 Wh you can spend. Turn that into clear, personal numbers with two inputs: your device’s battery size or watt draw. Use the simple formulas above to plan days away from outlets, choose the right cable, and decide whether you need higher output or just more energy. Keep it cool, charge one thing at a time when you can, and you’ll squeeze the maximum life out of every watt-hour.