How to Choose the Right Power Bank for Laptop Charging
Understanding watt-hours and output for efficient laptop charging.
1Understanding Watt-Hours
Power banks are often marketed with milliamp-hour (mAh) ratings, but watt-hours (Wh) provide a more accurate measure of capacity, especially for high-drain devices like laptops. To convert mAh to Wh, multiply by the voltage (typically 3.7V for lithium-ion cells). For example, a 10,000 mAh bank stores roughly 37Wh. This conversion helps compare energy storage across devices.
2Laptop Battery Capacity
To determine if a power bank can charge your laptop, first check your laptop’s battery capacity in Wh, usually found on the manufacturer’s website. For instance, MacBook batteries range from ~37Wh to 100Wh. A 10,000 mAh (37Wh) power bank may not fully charge most laptops, highlighting the importance of matching capacities.
3Power Usage Estimation
Estimating your laptop’s average power usage helps gauge how long a power bank can extend runtime. Divide the battery’s Wh capacity by its runtime in hours. For example, a 70Wh battery lasting 5 hours averages 14W. This estimation varies based on tasks, with video rendering consuming more power than browsing.
4Charging Efficiency Loss
Charging isn’t perfectly efficient; energy is lost during voltage conversion and as heat. Fast charging standards like USB Power Delivery (PD) increase voltage, leading to higher losses. A general rule is 20% efficiency loss for normal charging, but fast charging can lose 30% or more. This reduces the effective capacity of the power bank.
5Calculating Runtime Extension
To estimate runtime extension, subtract efficiency loss from the power bank’s Wh capacity. For example, a 20,000 mAh (74Wh) bank with 30% loss has ~52Wh effective capacity. With a laptop averaging 14W, this extends runtime by ~3.7 hours. If the laptop draws more power than the bank provides, it supplements the internal battery.
6Output Wattage Matters
A power bank’s capacity doesn’t indicate its output wattage. A high-capacity bank with low output (e.g., 15W) may slow laptop drain or be rejected entirely. Look for USB-C PD labels, which indicate higher charging levels. Always check per-port output, as total output can be misleading when charging multiple devices.
7Hardware Compatibility
Ensure your laptop supports USB-C charging, as some ports handle data or accessories but not power. Verify the power bank supports USB-C PD at sufficient wattage. A basic 15W output may charge phones but not laptops drawing 65W+. Also, use cables rated for high-wattage power, as standard cables may not suffice.
8Choosing the Right Power Bank
For most users, a 20,000 mAh/74Wh power bank is a practical emergency option, while a 27,000 mAh/100Wh bank is ideal for extended use. In the U.S., 100Wh is the airline limit without approval. Ensure the bank, laptop, and cable support the required power level for efficient charging.
Original article: Engadget — How to Choose the Right Power Bank for Laptop Charging