mAh vs Wh: How to calculate the real autonomy of a power bank? (LymobileShop Guide 2025)

At LymobileShop , we often see the same question: “How many real recharges does 10,000 mAh give?” The answer depends on a key element that many people forget: the difference between mAh (electrical capacity) and Wh (energy). Understanding this duo is the basis for choosing an external battery adapted to your uses (smartphone, tablet, laptop, console) without making a mistake. In this 2025 guide, we show you a simple and reliable method, with formulas, examples, a table and practical advice .

Clear definitions: mAh, Wh, nominal voltage (3.7 V) vs output (5 V)

Most power bank batteries use Li-ion cells with a nominal voltage ≈ 3.7 V. Manufacturers often display the capacity in mAh measured at this cell voltage (e.g. 10,000 mAh at 3.7 V). However, your devices (smartphones, etc.) are recharged on the **USB** side (5 V, or variable USB-C/PD profiles). The battery must therefore convert the 3.7 V energy from the cells to an output voltage (5 V, 9 V, 12 V, 20 V, etc.): there are losses .

To compare power banks, it is more accurate to think in terms of Wh (watt-hours) , as Wh represents the total energy stored regardless of voltage. The conversion from mAh to Wh depends on the cell voltage (≈3.7 V). Conversely, Wh to “mAh at 5 V” requires taking into account losses and the new output voltage.

The step-by-step formula + concrete examples

Basic formula: Wh = (mAh × V) / 1000 (with V ≈ 3.7 V for Li-ion cells)

• 5000 mAh → 5000 × 3.7 / 1000 ≈ 18.5 Wh
• 10,000 mAh → 10,000 × 3.7 / 1000 ≈ 37 Wh
• 20,000 mAh → 20,000 × 3.7 / 1000 ≈ 74 Wh
• 26,800 mAh → 26,800 × 3.7 / 1000 ≈ 99.2 Wh (airplane battery)
• 30,000 mAh → 30,000 × 3.7 / 1000 ≈ 111 Wh

From battery (3.7V) to USB output (5V): “mAh at 5V”, how to estimate?

If you absolutely want to express an “equivalent capacity” on the 5 V USB side, you must start from the useful Wh after losses (see next section), then divide by 5 V:

mAh_eq_5V ≈ (Wh_useful / 5) × 1000

Simplified example (good quality wire, estimated yield of 85%):

• 10,000 mAh → 37 Wh theoretical → Wh useful ≈ 37 × 0.85 = 31.45 Wh .
• mAh equivalent to 5 V ≈ 31.45 / 5 × 1000 = ~6290 mAh “at 5 V”.

This is why a 10,000 mAh does not offer 10,000 mAh “USB side”: we convert the voltage and lose a little energy in the process.

Actual performance: conversion losses, cables, wireless

The efficiency of the chain (battery → electronics → cable → device) determines the energy actually available. Some benchmarks observed in practice:

• Quality USB-C wired charging : 80–90% depending on power bank, cable and wattage.
• Wireless/Magnetic (Qi/MagSafe/Qi2) : often 60–75% (more convenient, but more losses through heating and coupling).
• Higher wattages (PD 45–100 W) : slightly more variable output (more heat), especially if the cable is poor.

The cable is very important: a certified USB-C, with a suitable conductor (and e-marker if 5A), limits losses. Dirty/oxidized connectors or a cable that is too long/thin increase resistance and therefore losses. On the device side, charging management (PPS, PD, etc.) and temperature also influence performance.

How many recharges depending on your devices?

The method for estimating the number of refills is simple:

1. Convert powerbank to Wh .
2. Apply a realistic yield (eg 85% wired, 70% wireless).
3. Divide by the device's battery power (in Wh).

Most modern smartphones have between 11 and 17 Wh (depending on the model/screen/battery life). Many tablets are around 25–40 Wh . Ultraportable laptops are more in the 45–60 Wh range, and 15–16 inch laptops often go up to 70–99 Wh .

Concrete examples

• Powerbank 10,000 mAh → 37 Wh theoretical. Wired at 85% → ~31.5 Wh useful.
  Smartphone 12–15 Wh → ~2.1 to 2.6 full charges (depending on usage while charging).
• Powerbank 20,000 mAh → 74 Wh theoretical. At 85% → ~62.9 Wh useful.
  Tablet ~30 Wh → ~2.1 charges; smartphone 12–15 Wh → ~4.2 to 5.2 charges.
• Powerbank 26,800 mAh (≈99.2 Wh) : at 85% → ~84.3 Wh usable.
  Laptop 50 Wh → ~1.7 “full” theoretical recharge (in practice, depending on usage, the power bank may maintain the level rather than recharge to 100% during a heavy task).

For wireless , repeat the same calculations but with a lower efficiency (e.g. 70%). Our 10,000 mAh (37 Wh) would give ~25.9 Wh useful → ~1.7 to 2.3 smartphone recharges of 12–15 Wh.

Special cases

• Charging while playing/filming : the device consumes power while charging; you “burn” some of the energy on live usage.
• Climate : in very cold or very hot weather, efficiency decreases.
• Aging : After hundreds of cycles, the capacity of the power bank (and your devices) decreases.

Quick conversion table mAh → Wh (express reference)

Standard assumption: cells at 3.7 V.

Capacity (mAh)	Energy (Wh)	Estimated useful Wh (85% wired)	Estimated useful Wh (wireless 70%)
5,000	18.5	15.7	13.0
10,000	37.0	31.5	25.9
15,000	55.5	47.2	38.9
20,000	74.0	62.9	51.8
26,800	99.2	84.3	69.4
30,000	111.0	94.4	77.7

LymobileShop Tip: If you're flying, aiming for ≤ 100 Wh makes life easier (26,800 mAh ≈ 99.2 Wh). Beyond that, some airlines require prior approval, and >160 Wh is prohibited for passengers.

Common mistakes to avoid

1. Confusing mAh “3.7V cells” and mAh “at 5V USB” : they are not the same thing. Thinking in Wh avoids pitfalls.
2. Forget about performance : low-end wireless or cable → less real battery life.
3. Neglecting power (W) : even with a lot of Wh, a 10 W output will not efficiently charge a laptop.
4. Ignore usage while charging : playing/filming consumes; the net “recharge” will be less.
5. Wrong cable : For 100–140 W USB-C PD, you need a 5A cable with e-marker .

LymobileShop advice for choosing the right one

• Define your needs : smartphone (daily), weekend/tablet, or laptop.
• Choose the right Wh + W duo :
  — Daily: 10,000–15,000 mAh (37–55 Wh), 20–30 W.
  — Versatile: 20,000 mAh (74 Wh), 30–45 W.
  — Laptop: 26,800–30,000 mAh (~99–111 Wh), 65–100–140 W depending on the PC.
• Wired first for speed/efficiency; add magnetic for convenience.
• Focus on safety : BMS protections, certifications, reliable materials.
• Take good cables (certified USB-C, e-marker if 5A).

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Want to apply these calculations now? Check out our LymobileShop selections:

• External batteries (all capacities)
• Solar power banks
• PD-compatible USB-C cables & chargers

FAQ

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LymobileShop : your e-commerce partner for reliable, high-performance, and safe power banks. Need personalized advice? Contact us via the contact page and we'll guide you to the ideal capacity and power for your smartphone, tablet, or laptop.