# How to Choose the Right Power Bank for Your Laptop Understanding watt-hours and output power for effective laptop charging. - **Source:** [Engadget - Technology News & Expert Reviews](https://brifing.si/source/16dd2da6-3eea-4d1e-b34f-45e846cdf037) - **Published:** 2026-09-27 - **Original article:** - **On Brifing:** https://brifing.si/s/947059bc-cceb-4125-ae38-a2be9a79c5e7 ## Watt-hours vs. mAh Power banks list capacity in milliamp-hours (mAh), but watt-hours (Wh) are the true measure of energy storage. To convert mAh to Wh, multiply by the voltage (typically 3.7V for lithium-ion cells) and divide by 1,000. For example, a 10,000 mAh bank stores about 37Wh. This conversion is crucial because laptops, being high-drain devices, require more energy than phones. ## Laptop battery ratings To estimate how much a power bank can charge your laptop, first find your laptop's Wh rating (usually on the manufacturer's site). Divide this by the battery's runtime to estimate average power usage. A 70Wh battery lasting 5 hours averages 14W. Note that actual usage varies—rendering video consumes far more power than browsing documents. ## Charging inefficiency Power banks lose energy during charging due to heat and voltage conversion. While 20% loss is typical for standard charging, fast charging (like USB Power Delivery) can see 30% or more. For a 20,000 mAh (74Wh) bank, this means only ~52Wh effectively reaches your laptop. Always account for this when calculating extended runtime. ## Output power matters A power bank's capacity doesn't indicate its output capability. A 50,000 mAh bank rated at 15W will barely slow a laptop's drain or may be rejected entirely. Look for USB-C PD (Power Delivery) labels, which ensure negotiation of higher charging levels. For most laptops, 45W+ output is necessary for effective charging. ## Per-port output details Total output ratings can be misleading. A bank labeled '100W total' might split this across ports or reduce output when charging multiple devices. Always check per-port specifications—your laptop needs consistent high wattage (e.g., 65W+) from a single port to charge properly during use. ## Cable requirements Not all USB-C cables support high-wattage charging. Standard cables handle up to 3A (60W at 20V), while 100W+ requires 5A-rated cables. For USB PD 3.1's 240W capability, all components (bank, laptop, cable) must support it. Avoid old or damaged cables that can't meet modern power demands. ## Ideal capacity choices A 20,000 mAh (74Wh) bank suits emergency top-ups, while 27,000 mAh (100Wh) offers near-full charges for most laptops. Note that 100Wh is the maximum airline-approved capacity without special permission. Larger banks exist but may be impractical for travel due to size and weight. ## Compatibility checks Ensure your laptop supports USB-C charging—some ports are data-only. Verify the bank's PD output matches your laptop's needs (e.g., 65W+ for MacBook Pros). If the laptop draws more power than the bank provides, it will supplement with internal battery, slowing drain rather than charging effectively. ## Sources covering this story - https://www.engadget.com/2266595/how-powerful-power-bank-needs-to-be-charge-laptop/ — --- _Summary written by Brifing from the original reporting. Copyright in the original article belongs to its publisher; read the full piece at the link above._