A power bank is easy to buy and surprisingly easy to buy badly. Two models may both claim 20,000 mAh, yet differ in charging speed, usable capacity, heat control, port quality and safety. In Bangladesh, where load shedding, travel and long commutes can make portable power genuinely useful, the best choice is the one that matches your devices—not the biggest number on the box.
Start with the capacity you actually need
Capacity is usually printed in milliamp-hours (mAh), but the advertised battery-cell capacity is not the exact amount that reaches your phone. Voltage conversion, cable loss and heat reduce usable energy. Treat the printed figure as a comparison point, not a promise of a precise number of full charges.
| Typical size | Best for | Trade-off |
|---|---|---|
| 5,000 mAh | Emergency top-ups and light travel | Small reserve |
| 10,000 mAh | Most phone users and daily carry | Balanced size and capacity |
| 20,000 mAh | Multiple devices, travel or outages | Heavier and slower to recharge |
| Above 20,000 mAh | Specialised use | Bulky; airline limits need attention |
For a normal phone user, a reputable 10,000 mAh model is often more practical than an unknown 30,000 mAh product.
Check output power, not only mAh
Charging speed depends on watts (W) and a compatible charging standard. A bank that supports USB Power Delivery (USB-PD) can negotiate suitable power with many modern USB-C devices. Some Android phones also use brand-specific fast-charging systems, so read the phone’s official specifications.
Look for clearly printed input and output ratings. A USB-C port marked “input only” cannot charge your phone. If you want one cable for both recharging the bank and charging a device, confirm that the USB-C port supports input and output.
How many watts do you need?
- Standard phone charging: a basic output may be enough, but slower.
- Fast-charging phones: match the phone’s supported protocol and wattage.
- Tablets: benefit from higher USB-PD output.
- USB-C laptops: require a bank specifically designed for laptop output; many phone banks cannot do this.
Use a simple Wh calculation
Airlines and safety guidance often use watt-hours (Wh), not mAh. If Wh is not printed, the approximate calculation is:
Wh = (mAh × battery voltage) ÷ 1000
Using the common nominal cell voltage of 3.7 V, a 20,000 mAh bank is about 74 Wh. Check the rating printed by the manufacturer because construction can differ.
Power-bank rules when flying
Current FAA and IATA guidance says spare lithium batteries and power banks belong in carry-on baggage, not checked baggage. Up to 100 Wh is generally allowed; 100–160 Wh may require airline approval, and larger batteries are generally not permitted on passenger aircraft. Individual airlines and countries can impose stricter rules, so check your airline before leaving Bangladesh.
Protect the terminals, keep the bank accessible and stop using it if it swells, overheats, leaks or smells unusual.
How to identify a safer product
- Choose a known manufacturer or a seller that provides a real invoice and warranty.
- Confirm that model numbers and electrical ratings are printed clearly.
- Avoid unrealistic capacity claims in a very small, light body.
- Look for protection against overcharge, over-current, short circuit and excessive temperature.
- Check that the casing is rigid, ports do not move and the cable fits firmly.
- Do not buy a damaged, swollen or heavily used lithium battery.
A low price is not a saving if the bank damages a phone or becomes a fire risk. Compare warranty, seller reputation and electrical specifications—not only marketplace reviews.
Choose the cable carefully
A poor cable can limit speed or become hot even when the bank is capable. Use a cable rated for the required current and protocol. For higher-power USB-C charging, use a correctly rated cable from a reliable source. Replace cables with bent connectors, exposed wire or loose plugs.
How to test a new power bank
- Inspect the body and ports before charging.
- Recharge it using the recommended input.
- Charge one device while keeping the bank on a hard, ventilated surface.
- Check whether the phone shows the expected fast-charging mode.
- Feel for abnormal heat at the bank, cable and connector.
- Repeat across the ports you plan to use.
- Keep the invoice and packaging through the return period.
Battery care that improves useful life
Keep the bank away from direct sun, parked cars and water. Do not cover it with bedding while charging. If it will be stored for a long time, follow the manufacturer’s storage instructions and check it periodically. Do not pierce, crush or attempt to replace internal cells yourself.
If you need a reliable connection during power cuts as well, see SiteChai’s guide to testing internet speed and fixing slow Wi-Fi in Bangladesh. For a business website that must remain reachable, SiteChai’s web-hosting plans include practical hosting features and local support.
Frequently asked questions
Is 20,000 mAh allowed on a flight?
It is commonly below 100 Wh when based on typical 3.7 V cells, but rely on the printed Wh rating and your airline’s current rules.
Can a power bank charge a laptop?
Only if it provides the wattage and USB-PD profile the laptop requires. A USB-C connector alone is not proof.
Why does a power bank not deliver its full advertised mAh?
The cell rating and the energy delivered after voltage conversion are different. Conversion losses and heat reduce usable output.
Is wireless power-bank charging better?
It is convenient, but usually less efficient and can create more heat than a good cable. Choose it for convenience, not maximum efficiency.
Sources: FAA lithium-battery guidance and IATA passenger battery guidance, checked 26 August 2026.