How long do power banks actually last? The honest answer

What the mAh number actually means

The mAh printed on a power bank is the capacity of the internal battery at its cell voltage — usually 3.7V. But your phone charges at 5V. That means a significant portion of the rated capacity is used up in the conversion. A "20,000mAh" power bank delivers closer to 12,000-14,000mAh at the USB port. This is not a scam — it is physics.

Real-world capacity: the honest math

If a power bank claims 20,000mAh, expect it to charge a modern smartphone (around 5,000mAh battery) roughly 2.5 to 3 times from zero. If it charges your phone five times, either the phone has a small battery or the power bank is overstating its capacity. The middle path is usually the honest one.

• 10,000mAh power bank — approximately 1.5 full charges of a modern phone.
• 20,000mAh power bank — approximately 3 full charges.
• 30,000mAh power bank — approximately 4.5 to 5 full charges.
• Above 30,000mAh — usually branded for laptops or multi-device use.

How long before the battery wears out

Lithium-ion and lithium-polymer batteries degrade over time. A good power bank should retain 80% of its original capacity for 500-800 full charge cycles. For the average user, that is 2-4 years of regular use. Cheap power banks with low-quality cells degrade much faster — some lose half their capacity within a year.

What shortens the life of a power bank

Heat is the biggest enemy. Leaving a power bank in a hot car, charging it in direct sunlight, or charging it and discharging it at the same time (charging your phone while the power bank is plugged into the wall) all accelerate wear.

• High heat — never leave a power bank in direct sun or a hot car.
• Simultaneous charge and discharge — avoid it where possible.
• Deep discharge — charge the bank before it drops to zero.
• Cheap cells — the biggest variable. A well-built power bank with good cells outlasts a cheap one by 3-4x.

How to tell a good power bank from a bad one

You cannot tell by looking. The brand name is often meaningless — most power banks are made in a handful of factories and rebranded. What you can check is the real-world charge count. Buy from a seller with a return policy, test it within the return window, and if it does not deliver the promised capacity, return it. That is the only honest test.

Fast charging and pass-through charging

Two features are worth paying for. Fast charging (PD or QC) means the power bank recharges quickly and charges your phone quickly. Pass-through charging means you can charge your phone through the power bank while the power bank is plugged into the wall. Both extend usefulness without adding much to the price.

What to look for when buying

A power bank is a purchase you should make carefully, because the return experience is often frustrating. Look for clear capacity claims, honest product photos, and a seller with a real support process.

• Realistic capacity — a 20,000mAh bank should deliver about 3 full charges.
• USB-C input and output — the modern standard.
• At least 20W fast charging if your phone supports it.
• A visible capacity indicator — so you know when it needs charging.
• A seller with a return policy — the only reliable safety net.