How Many Charges From A Power Bank? | Charge Math

You came here to figure out how many full recharges a battery pack can deliver to your phone, tablet, or laptop. Here is the short version: convert the bank’s capacity to watt-hours, multiply by a realistic efficiency, then divide by your device battery in watt-hours. That single line gets you a number you can trust, and it takes under a minute.

How Many Phone Recharges From A Power Bank: The Quick Math

The math is simple once you use energy units. Most packs print milliamp-hours at a nominal cell voltage. Energy equals watt-hours, so convert with Wh = (mAh × V) ÷ 1000. Pick an efficiency between 0.7 and 0.85 for decent gear. Then use Charges ≈ Bank Wh × Efficiency ÷ Device Wh. Round down because phones and laptops taper near full and stop early.

Fast Reference Table For Common Sizes

To ground the method, the table below shows rough phone recharges from common pack sizes. Phone energy assumes a 12.0–12.9Wh battery, which matches many midrange models. Values use 80% efficiency. Swap your own numbers if your phone sits above or below that range.

Bank Label (mAh @ V)	Energy (Wh)	Est. Phone Recharges*
5000 @ 3.7	18.5	~1.2
10000 @ 3.7	37.0	~2.4
20000 @ 3.7	74.0	~4.7
26800 @ 3.7	99.16	~6.3

*Assumes 80% efficiency and a ~12.5Wh phone. Round down for real use.

What Changes The Recharge Count

Real life bends the result. Voltage conversion, cable losses, and fast-charge overhead eat into the headline capacity. Battery age matters too. Cool, gentle charging preserves capacity; heat and deep cycles do the opposite. USB-C Power Delivery also changes charge speed and heat, not energy, so the count stays similar while the time drops.

Where Efficiency Goes

Where does the missing energy go? Your bank steps cell voltage up to five, nine, or higher, then your phone drops it down to charge the internal cell. Every conversion wastes a slice. Coils, controllers, and cables warm up, and that warmth is lost energy. Good packs with PD or well tuned buck-boost stages land near 80–85%. Small banks or wireless pads fall lower.

Find Your Device Battery In Wh

If your device lists only milliamp-hours, you can still get watt-hours. Most phones use cells rated around 3.7 to 3.87 volts. Multiply the mAh by that voltage and divide by one thousand. A 5000mAh phone at 3.85V holds about 19.25Wh. Laptops already list Wh on spec pages or labels under the base. Tablets often sit between 20 and 35Wh.

Phones, Laptops, Tablets, And Tiny Gadgets

Bigger gadgets need bigger energy budgets. A 65Wh ultrabook will drain a small pack in a blink. Match a laptop with a bank that lists watt-hours on the label and supports the right PD profile. For earbuds and watches, even a slim pack offers dozens of top-ups because their batteries are tiny.

Three Quick Scenarios

Let’s run three quick scenarios. First, a 20000mAh bank with 3.7V cells holds 74Wh. At 80% efficiency you have 59.2Wh to spend. With a 12.5Wh phone you’ll see around four full top-ups. Second, a 10000mAh pocket bank equals 37Wh; the same phone nets about two and a bit. Third, a 24Wh tablet from a small bank will see a single full charge with a little left.

Simple Habits That Boost Real-World Results

You can squeeze more from the same gear with a few habits. Charge at room temperature. Use short, certified cables with tight connectors. Skip tiny trickle sessions; top up from around twenty to eighty percent to limit heat. Avoid wireless pads if the goal is count; they waste extra energy. Keep banks in carry-on when you fly and check airline rules.

Trusted Rules And Standards

Air travel policies and charging specs refer to energy, not just mAh. See the IATA guidance on the watt-hour rating and the USB-IF overview of USB Power Delivery for context on power levels and profiles.

Losses You Should Expect

This reference table lists the usual loss factors and how much they dent your total. Use it to sanity-check a bold capacity claim on a product page.

Loss Factor	Typical Range	What It Means
DC-DC Conversion	10–20%	Voltage step-up in the bank and step-down in the device waste energy.
Cable Resistance	1–5%	Thin or long cables heat up; use certified short USB-C cords.
Fast-Charge Overhead	2–8%	Higher current raises heat; energy stays the same, time drops.
Wireless Charging	30–50%	Coil coupling losses cut delivered energy.
Low Temperature	5–15%	Cells resist flow in cold conditions; keep gear warm.
Device Taper Near Full	3–10%	Charge current falls at high state of charge; sessions end early.

When Numbers Do Not Match Your Experience

Math meets the real world in edge cases. Some packs overstate capacity by quoting cell mAh without clarifying voltage, which inflates expectations. Some phones draw a fee for fast modes and warm up; that cost shows up as fewer recharges. Old batteries inside phones or banks also sag under load and end charging early.

Step-By-Step Calculator Method

Want a quick repeatable process? Grab the bank label and your device specs and run these steps any time you shop or pack for a trip.

Five Steps You Can Use

1. Find bank Wh from the label or convert from mAh at the cell voltage.
2. Pick an efficiency based on gear quality; 75–85% covers most cases.
3. Find your device Wh; convert if needed.
4. Divide and round down.
5. Adjust five to ten percent for cold weather, old batteries, or wireless pads.

mAh Versus Wh In Plain Terms

milliamp-hours describe charge, not energy. Two packs with the same mAh can store different energy if their cell voltages differ. Energy is the unit that lines up with work done, which is why watt-hours unlock fair comparisons. Retail packaging loves big mAh numbers because they look friendly; the science runs on watt-hours.

Why Nominal Voltage Matters

Nominal voltage is a rated midpoint, not a constant. A lithium-ion cell starts near 4.2V and glides down past 3.5V during discharge. Manufacturers use a standard nominal figure, often 3.7V or 3.85V, to keep conversions consistent. When a bank lists 20000mAh at 3.7V, the energy equals 74Wh. If the same pack used a 7.4V internal series setup, the printed mAh would be smaller, while Wh stays the same. That is why power budgets should live in Wh.

Charge Speed, PD Profiles, And Count

Power Delivery adds negotiation between the bank and the device. It lets a laptop request 20V at 3A, while a phone might ask for 9V at 2A. Charge speed depends on the agreed profile and the cable rating. Faster charging creates more heat, which trims efficiency a little. Energy in and out still follows the same math, so the number of recharges does not leap just because watts are higher.

How To Read A Bank Label

A good label shows both mAh and Wh. You may also see the rated capacity at 5V USB output, which already accounts for conversion losses at a set load. That output figure tends to be lower than the cell energy because of heat and circuitry. Prefer brands that publish clear Wh and supported PD levels such as 20V-3A or 28V-5A.

Common Math Mistakes

Common mistakes lead to wrong expectations. One is mixing mAh between different voltages. Another is ignoring efficiency and cable losses. A third is comparing a phone set to fast mode against a friend’s phone on a slow charger, then blaming the bank. The method here avoids all three by staying in watt-hours.

Travel Rules That Matter

Airlines and regulators care about energy, not mAh. Carry spare lithium packs in your cabin bag. Most carriers cap standalone banks at 100Wh before asking for approval; many allow up to 160Wh with permission. Airlines may also forbid in-flight use even when carriage is allowed. Check the label before you fly and keep terminals covered. See the TSA rules for power banks for U.S. screening specifics.

Worked Examples You Can Copy

Here are detailed walk-throughs you can mirror with your own gear. Case A: a 26800mAh bank built on 3.7V cells. Energy equals 99.16Wh. Using 80% gives 79.33Wh to spend. A phone near 12.5Wh gets six full top-ups with a slice left for a smartwatch. Case B: a compact 10000mAh pack. Energy equals 37Wh; with 75% efficiency you get 27.75Wh. A large 19Wh phone charges once, then reaches about forty-five percent on the second cycle. Case C: a 65Wh laptop on a 100Wh bank that supports 20V-5A PD. At 85% the usable pool is 85Wh, so you can almost refill the laptop once, with a small buffer for a phone.

Device Battery Size Ranges

Typical phone batteries range from about 10 to 17Wh. Tablets span a wide band from 20 to 45Wh. Light laptops use 50 to 70Wh, while creator rigs sit between 80 and 99Wh. Smartwatches float under 1Wh and earbuds cases hover around 1 to 3Wh. Knowing these ranges helps you sanity-check any marketing claim.

Troubleshooting Low Counts

If your result feels off, verify three items. First, confirm the bank energy in Wh; avoid relying only on printed mAh. Second, check the cable and port. A weak cable drops voltage and raises heat, wasting energy. Third, reset fast-charge modes and try a lower profile to see if the count changes. Large swings point to a tired device battery or an overstated bank label.

Buying Guide In A Nutshell

When shopping, start with energy, not slogans. Pick a bank with published Wh and a label that lists PD levels that match your devices. Look for 5A USB-C cables if you plan to run high power. Prefer brands that publish efficiency tests or output capacity at five volts and at PD levels. Extra ports are handy, yet remember that charging two phones at once splits the pool.

Pocket Method Card

Here is a compact card you can save. Step 1: find bank Wh from the label or convert from mAh at the cell voltage. Step 2: pick an efficiency based on gear quality; 75–85% covers most cases. Step 3: find your device Wh; convert if needed. Step 4: divide and round down. Step 5: adjust five to ten percent for cold weather, old batteries, or wireless pads.

Safety Notes You Should Follow

Safety sits above convenience. Use banks that list built-in protections such as over-current, short-circuit, and thermal cut-off. Do not charge under a pillow. Keep vents clear and stop using any pack that swells or smells odd. On trips, place the bank in a spot you can reach, not in a checked suitcase. Airline and aviation bodies post rules that focus on watt-hours and proper packaging, so labels matter.

Care And Storage Tips

Good care keeps both the count and the pack healthy. Store near half charge if you will shelve the bank for weeks. Top it up every few months. Avoid full discharges on tiny models; they struggle at the end of the curve. Wipe ports so lint does not block pins. Match the cable to the job: slim cords work for earbuds, not for a gaming laptop.

Common Myths, Debunked

A few myths keep circulating. Fast charging does not add energy; it only changes time. A bigger number in mAh does not always beat a smaller one if the voltage differs. Wireless charging is convenient yet wastes energy; use it when count does not matter. Leaving a bank plugged in all night is a bad habit; unplug when the device hits your target level now.

Final Take

You now have a clear method that turns a vague claim on a box into a reliable estimate. Do the watt-hour conversion, apply a sane efficiency, divide by your device battery, and round down. That gives you a recharge count you can plan around.