Home/Blog/Power Banks/Power Bank Buying Guide: How Many mAh Do You Actually Need?

Power Banks

Power Bank Buying Guide: How Many mAh Do You Actually Need?

The mAh number on a power bank’s box is measured under lab conditions that have almost nothing to do with how it charges your iPhone. Voltage conversion losses alone typically eat 20-30% of that number before it ever reaches your battery. Here’s how to translate the label into something useful.

Tiny Tech Box Team · Aug 6, 2026 · 6 min read

The rough math

A modern iPhone battery holds somewhere between 3,000 and 4,500 mAh depending on the model. A power bank rated at 10,000mAh will realistically deliver about 6,500-7,500mAh of usable charge — roughly one and a half to two full iPhone charges, not “three charges” as some listings imply.

Quick reference

5,000mAh ≈ one partial top-up. 10,000mAh ≈ 1.5-2 full charges. 20,000mAh ≈ 3-4 full charges, but adds real pocket weight.

Match the size to how you'll use it

A pocket-size 5,000mAh bank is enough for most single-day top-ups and is the one people actually remember to carry. A 20,000mAh brick makes sense for multi-day travel, but it’s the one that ends up left in a drawer if it’s too bulky for daily use.

Don't ignore output wattage

Capacity gets all the marketing attention, but output wattage determines how fast that capacity actually reaches your phone. A high-mAh bank with a weak output port will still charge slowly — check the watts, not just the mAh, before you buy.

Bottom line

Buy the smallest capacity that covers your actual daily gap, not the biggest number you can find. The power bank you’ll actually carry beats the one that promises the most charges on paper.