How to Choose the Right Power Bank Capacity for Your Needs

Power banks range from tiny 5,000mAh sticks to massive 26,800mAh bricks, and the marketing makes it seem like bigger is always better. But carrying a power bank you don't need is carrying dead weight. Here's how to calculate exactly what capacity you need.

Understanding mAh (Milliamp-Hours)

A power bank's capacity is measured in milliamp-hours (mAh). This tells you how much electrical charge it stores. But there's a catch: you don't get 100% of the rated capacity.

The 70% rule: Due to voltage conversion losses and heat, a power bank delivers roughly 60-70% of its rated capacity to your device. A 10,000mAh power bank actually delivers about 6,000-7,000mAh of usable charge.

How to Calculate Your Needs

Step 1: Know Your Device Batteries

| Device | Typical Battery | |--------|----------------| | iPhone 15 | 3,349mAh | | iPhone 15 Pro Max | 4,441mAh | | Samsung Galaxy S24 | 4,000mAh | | Samsung Galaxy S24 Ultra | 5,000mAh | | iPad Air | 7,607mAh | | iPad Pro 11" | 7,538mAh | | AirPods Pro case | 523mAh | | Nintendo Switch | 4,310mAh | | Apple Watch | ~300mAh |

Step 2: Count Your Charges

How many full charges do you need before you can access a wall outlet?

Daily commuter (home → office → home): 1 phone charge. That's about 4,000-5,000mAh of usable power needed, so a 5,000-10,000mAh power bank is plenty.

Day trip (out all day): 2 phone charges plus maybe earbuds. About 8,000-10,000mAh usable, so a 10,000-15,000mAh power bank.

Weekend trip: 3-4 phone charges, tablet charge, earbuds. About 20,000mAh usable, so a 20,000-26,800mAh power bank.

International travel: Maximum capacity. You might not find an outlet for 12+ hours.

Step 3: Factor in Size and Weight

| Capacity | Weight | Size | Charges (iPhone 15) | |----------|--------|------|-------------------| | 5,000mAh | 4 oz | Lipstick-sized | ~1 charge | | 10,000mAh | 7 oz | Deck of cards | ~2 charges | | 20,000mAh | 13 oz | Small book | ~4 charges | | 26,800mAh | 18 oz | Large book | ~5 charges |

Our Picks by Use Case

Pocket-Sized EDC (Every Day Carry)

The Anker 621 MagGo 5,000mAh ($23) magnetically attaches to the back of any MagSafe-compatible iPhone. It adds one full charge and weighs just 4 ounces. You don't even feel it in your pocket.

The Goldilocks (Most People)

The Anker 523 Power Bank 10,000mAh ($21) delivers two full phone charges with two USB-C ports for simultaneous charging. It supports 20W fast charging, so your phone charges almost as fast as from a wall outlet.

The Road Warrior

The Anker 737 Power Bank 24,000mAh ($95) is a beast — 140W output that can fast-charge a MacBook Pro, 24,000mAh capacity for 5+ phone charges, and a built-in display showing remaining capacity. It's heavy (1.3 lbs) but replaces the need to carry a laptop charger on short trips.

The Laptop Charger

For charging laptops, you need both high capacity AND high wattage output. The power bank must explicitly support USB-C PD (Power Delivery) at your laptop's required wattage.

The Baseus Blade 100W 20,000mAh ($65) is impressively thin (0.7 inches), charges most laptops at full speed via 100W USB-C PD, and its flat form factor slips into a laptop bag without adding bulk.

Charging Speed Matters

A power bank that takes 12 hours to recharge itself is impractical. Look for these fast-charge specs:

Input speed (how fast it recharges): 18W minimum. 30W or higher is ideal. A 20,000mAh bank at 18W takes about 6 hours to recharge. At 30W, about 3.5 hours.

Output speed (how fast it charges your phone): 20W is the standard for fast-charging modern phones. 65-100W is needed for laptops.

Airline Regulations

The TSA and most airlines limit carry-on power banks to 100Wh (approximately 27,000mAh at 3.7V). Power banks above this require airline approval. All the picks above fall within the 100Wh limit.

Important: Power banks must go in carry-on luggage, never checked bags. This is a universal aviation safety rule.

Pro Tips

1. Don't let it drain to 0%. Store power banks between 20-80% charge when not in use. Deep discharge shortens lithium battery lifespan.
2. Keep it cool. Don't leave power banks in hot cars. Heat accelerates battery degradation.
3. Look for passthrough charging. Some power banks can charge your phone while the power bank itself is charging from the wall. This turns it into a USB hub at your hotel.

Read our full power bank guide →

Read our full USB-C charger guide →

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