A 20,000 mAh power bank typically delivers 3–6 phone recharges, depending on battery size and efficiency.
You bought a chunky pack because you want days of phone time without a wall outlet. The next step is setting expectations. Pack labels speak in milliamp-hours, phones drink energy in watt-hours, and there are conversion losses in between. This guide turns that into a clear range you can trust, plus a quick method you can reuse for any device.
Charge Count From A 20,000 mAh Power Bank—At A Glance
Start with energy, not just milliamp-hours. Inside most packs, lithium cells sit near 3.7 volts. Multiply amp-hours by that voltage to get energy in watt-hours, then account for conversion losses on the way to your device. A 20,000 mAh pack equals about 74 Wh before losses. With real-world efficiency, you can expect only a slice of that number to reach your phone or tablet.
Broad Estimate Table For Popular Devices
The table below assumes end-to-end efficiency between 65% and 75% from pack to device. Your number shifts with cable quality, charge speed, screen-on time while charging, and battery health. Use it as a quick reference, then read on for the exact math.
| Device Type | Typical Battery (mAh or Wh) | Expected Full Recharges |
|---|---|---|
| Compact Phone | 3,000–3,300 mAh | 5–6 |
| Mid-Size Phone | 3,700–4,000 mAh | 4–5 |
| Large Phone | 4,500–5,000 mAh | 3–4 |
| Small Tablet | 7,000–8,000 mAh | 2–3 |
| Wireless Earbuds Case | 500–600 mAh | 30–40 |
| Smartwatch | 300–400 mAh | 50–70 |
| Handheld Console | 5,000–7,000 mAh | 2–3 |
| USB-C Laptop (thin-and-light) | 40–55 Wh | ~1 |
How The Math Works (So You Can Reuse It)
Step 1: Convert The Pack Label To Watt-Hours
Use the standard industry formula: Wh = Ah × V. A “20,000 mAh” pack is 20 Ah. Multiply by 3.7 V and you get about 74 Wh of stored energy. That formula is the same one used in airline battery rules, and it’s the most honest way to compare capacities across devices.
Step 2: Apply Real-World Efficiency
Energy isn’t delivered at 100%. Inside the pack, a boost converter raises 3.7 V to the USB output. The device then steps that down again to charge its cells. Heat and regulation overhead shave off a chunk at both stages. Major brands cite conversion near the low-80s percent inside the pack, with more loss on the device side. End-to-end, a practical range lands around 60%–75% of the raw watt-hours.
Step 3: Divide By Your Device’s Battery Energy
Now split the usable watt-hours by the energy your device stores. Many Android flagships sit near 5,000 mAh at about 3.85–4.4 V nominal, while some compact phones sit near 3,300 mAh. Tablets are larger again. If a phone battery holds roughly 15–19 Wh, a usable 50–56 Wh from a 20,000 mAh pack yields three to six full refills.
Worked Examples You Can Mirror
Example A: 5,000 mAh Phone
Pack energy ≈ 74 Wh. Assume 70% end-to-end efficiency → usable ≈ 51.8 Wh. A 5,000 mAh phone at 3.85 V stores about 19.3 Wh. 51.8 ÷ 19.3 ≈ 2.7. Round that to roughly three full refills before the pack is empty.
Example B: 3,700 mAh Phone
Usable energy again ≈ 51.8 Wh. A 3,700 mAh phone at 3.85 V stores about 14.2 Wh. 51.8 ÷ 14.2 ≈ 3.6. That’s around three to four refills, with a bit left over for a small accessory.
Example C: Small Tablet At 28 Wh
Some compact tablets sit near 25–30 Wh. Using the same 51.8 Wh usable figure, that’s roughly one and a half to two complete charges. Expect fewer if the screen stays on while topping up.
What Changes The Count In Real Life
Charge Speed And Heat
Fast USB-C Power Delivery can waste more power as heat, especially at high voltages. When you push 20 V or high current, conversion efficiency dips. Slower rates are kinder to both the pack and the phone, and they return a bit more energy per watt-hour stored.
Cable Quality And Length
Thin, long, or worn cables add resistance. That turns some power into heat instead of battery fill. A short, certified cable trims those losses and helps the pack run cooler.
Screen-On And Background Use
Navigation, gaming, or streaming during a charge steals watt-hours that never reach the battery. If you’re charging while using the device, expect one fewer refill across a weekend.
Battery Health
Older phone batteries accept energy less efficiently and sag earlier near full. Brands also design batteries to keep around 80% of original capacity after a defined cycle count. That means a two-year-old handset may show fewer full refills from the same pack.
Charge Count For A 20,000 mAh Pack—Phone, Tablet, And Laptop
Now plug numbers into a second table that matches real travel days. Swap values to mirror your gear list.
| Use Case | Assumptions | Estimated Refills |
|---|---|---|
| Weekend Trip, One Large Phone | 5,000 mAh phone, screen mostly off while charging, 70% efficiency | ~3 phone refills |
| Day Hike, Two Phones | 4,000 mAh + 3,700 mAh phones, 65% efficiency, some screen-on time | ~5 total refills |
| Commute + Earbuds | 4,500 mAh phone plus 500 mAh earbuds case | ~3 phone refills + many earbud top-ups |
| Light Laptop Sips | 45 Wh ultrabook, USB-C PD at 15–20 V | ~1 full laptop refill or partial top-ups |
| Console Session | 6,000 mAh handheld, played while charging | ~1–2 refills |
Picking The Right Pack For Your Gear
Match Output To Your Devices
Capacity is only part of the story. A phone that supports 25–45 W PD needs a port and cable that can deliver it. Laptops often need 45–65 W or more. If your pack tops out at 18 W, the refill count stays similar, but each session takes longer and generates less heat.
Look For Honest Specifications
Quality brands publish watt-hours alongside milliamp-hours, show rated capacity at 5 V for USB outputs, and disclose efficiency ranges. Some even explain why a pack with cells rated at 20 Ah cannot provide 20 Ah at 5 V, because the boost step trades current for voltage and wastes a slice as heat. Clear datasheets that show cell voltage, watt-hours, and 5 V rated capacity make comparisons fair and keep expectations realistic across brands and models.
Mind Airline Limits
Energy is what airlines care about. A 20,000 mAh pack at 3.7 V is about 74 Wh, which sits under the common 100 Wh threshold for carry-on. Many carriers permit spare packs up to 160 Wh with prior approval, so travelers rarely need paperwork at this size.
Calculate Your Own Refill Count
One Minute Method
- Convert pack label to watt-hours using Wh = Ah × 3.7 V.
- Multiply by 0.65–0.75 for a realistic usable range.
- Find your device battery in Wh (mAh × ~3.85 V ÷ 1000 for many phones; tablets often publish Wh directly).
- Divide usable Wh by device Wh to get expected full refills.
Example With Real Specs
Samsung lists 3,700 mAh for one model and 5,000 mAh for another, both at typical ratings. Using those figures keeps the math grounded in reality. Repeat the steps above with your own device and you’ll know what to expect before you pack for a trip.
Tips To Stretch Your Pack Further
Charge At Moderate Speeds
Use a port profile that meets your needs without going to the highest voltage. Lower heat improves efficiency and preserves both batteries over time.
Use Short, Certified Cables
Pick well-made USB-C cables for high-current sessions. Keep them under a meter when possible to cut resistive loss.
Top Up More Often
Shallow cycles are easier on lithium cells. Frequent top-ups on both the phone and the pack are better for longevity than deep drains.
FAQ-Style Clarifications, Without The FAQ Block
Why Doesn’t A 20,000 mAh Label Equal Four Full 5,000 mAh Refills?
Milliamp-hours are stamped at cell voltage, while your phone charges at higher system voltage. You also lose energy in the DC-DC converters in the pack and inside the phone. The only fair comparison uses watt-hours.
Why Do Some People Report Better Or Worse Results?
Two main reasons: different use while charging and different charge speeds. Game during a charge and you burn watt-hours that never reach the battery. Push 20 V PD on a warm day and conversion losses climb.
Is A Bigger Pack Always Better?
Only to a point. Larger banks add weight and take longer to refill. Pick capacity that matches your longest unplugged stretch plus a safety margin. For many travelers, 20,000 mAh hits a sweet spot between size and energy.
Bottom Line For Buyers
A 20,000 mAh bank translates to about 74 Wh on paper and roughly 45–56 Wh in your pocket after losses. For phones, that means three to six full refills based on battery size and how you charge. For small tablets, plan on one to two. With the quick method in this guide and a couple of real specs from your devices, you can predict your own number with confidence.