Power banks are sold almost entirely on one number: capacity. That number is also the one most often misunderstood and most frequently exaggerated. Knowing how to read a power bank specification saves you from buying something that delivers half of what it claims.
What mAh actually tells you
Capacity is quoted in milliamp hours. A 20,000mAh power bank does not deliver 20,000mAh to your phone. The rated capacity describes the internal cells, which operate at around 3.7 volts. Your phone charges at 5 volts or higher, and converting between them loses energy as heat.
Realistic delivered capacity is roughly 60 to 70 percent of the rated figure. A genuine 20,000mAh bank delivers somewhere near 13,000mAh in practice. That is not a defect; it is physics, and it applies to every power bank.
The practical implication: to charge a phone with a 5,000mAh battery about two and a half times, you need a bank rated around 20,000mAh, not 10,000mAh.
Spotting inflated claims
Capacity fraud is widespread. A useful sanity check is weight. Lithium cells have a fairly consistent energy density, so capacity and weight correlate closely.
A genuine 20,000mAh power bank weighs somewhere around 350 to 400 grams. If a listing claims 20,000mAh for a device weighing 150 grams, the claim is false. There is no technology that makes cells dramatically lighter at the same capacity.
Implausibly low prices are the other signal. Cells are the dominant cost in a power bank. A bank priced far below comparable products either contains fewer cells than claimed or uses recycled cells of unknown history.
Output: the number that determines charging speed
Capacity determines how many charges you get. Output determines how fast each one happens. These are independent, and a large bank with weak output charges slowly.
Look for the output wattage, or the voltage and amperage figures. A basic 5V/2A output delivers 10W, which is slow for a modern phone. Fast charging generally starts around 18W and goes up considerably from there.
Check which fast-charging standards the bank supports. Power Delivery (PD) and Quick Charge (QC) are the common ones. Your phone and the bank must support a shared standard for fast charging to engage. A PD phone paired with a QC-only bank falls back to slow charging.
If you want to charge a laptop or tablet, confirm the bank supports the wattage those devices need, which is typically much higher than a phone requires.
Input: how fast the bank itself refills
This specification is routinely ignored and genuinely matters. A large power bank with a slow input port can take most of a day to recharge.
Look for the input wattage and connector type. USB-C input with Power Delivery recharges dramatically faster than an older micro-USB input. If a 20,000mAh bank has only a 5V/2A micro-USB input, expect a very long recharge.
Some banks support pass-through charging, meaning they can charge a device while themselves being charged. Useful if you have one outlet, though it generates more heat.
Ports and practical use
Count the ports and check what each one does. Some banks have multiple outputs but share total power between them, so charging two devices halves the speed for each.
Check connector types. A bank with USB-C output serves modern phones directly. One with only USB-A outputs requires a cable with the right end for your device.
Confirm whether a cable is included and what type. Many banks ship with a short charging cable that is adequate for recharging the bank but inconvenient for use.
Safety: the part worth caring about
Lithium cells store significant energy, and poorly built power banks are a genuine fire risk. Quality units include protection circuitry against overcharge, over-discharge, short circuit, over-current and excessive temperature.
Warning signs in use include heat beyond mild warmth, swelling of the casing, a rattling sound indicating loose internal components, and any smell. A power bank that swells should be stopped immediately and disposed of properly, never punctured or thrown in general waste.
Do not charge a power bank overnight on soft surfaces such as a bed, and do not leave one charging unattended in a confined space.
Choosing a capacity
Think about your actual pattern rather than buying the largest available.
A 10,000mAh bank delivers roughly one and a half phone charges, weighs little, and fits a pocket. It suits daily carry as insurance against a flat battery.
A 20,000mAh bank delivers roughly two and a half to three phone charges and suits travel or days without reliable power. It is noticeably heavier.
Larger banks exist but become awkward to carry and slow to recharge. Beyond a point, two smaller banks are more practical than one large one.
Buying checklist
- Rated capacity, with weight as a plausibility check
- Output wattage and supported fast-charging standards
- Input wattage and connector type for recharge speed
- Number of ports and whether power is shared between them
- Stated protection features
- Included cable type and length
- Warranty terms and vendor contactability
Buying safely
Power banks are among the most counterfeited electronics sold online, and the fakes are more dangerous than most because of the fire risk. Convincing packaging costs almost nothing to reproduce.
Buy from vendors who state real specifications rather than a single headline capacity figure. Listings that quote capacity and nothing else should be treated with caution.
On Endinov, vendors maintain identifiable storefronts with order records, and payment runs through a protected channel, so you have a route to resolution if a unit does not match its description or fails early.
Compare power bank capacities, output wattages and charging standards from verified vendors on Endinov before buying.
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