Here are some key features and considerations when choosing a power bank:

1. Capacity: Measured in milliampere-hours (mAh), the capacity of a power bank determines how much charge it can hold. Higher capacity power banks can charge devices multiple times but are usually bulkier.

2. Output Power: This is measured in volts (V) and amperes (A). Higher output power results in faster charging. Common outputs include 5V/1A, 5V/2A, and even higher for fast-charging technologies.

3. Input Power: Determines how quickly the power bank itself can be recharged. Higher input power results in quicker recharges.

4. Number of Ports: Some power banks have multiple USB ports, allowing you to charge multiple devices simultaneously.

5. Size and Weight: There is a trade-off between capacity and portability. Larger capacity power banks tend to be heavier and bulkier.

6. Special Features: Some power banks come with additional features like LED indicators, built-in cables, wireless charging, and even solar panels.

7. Safety Features: Look for power banks with safety features such as overcharge protection, short circuit protection, and temperature control to ensure safe use.

Recommendations:

• Anker PowerCore 10000: Known for its compact size and reliable performance.
• RAVPower 26800mAh: High capacity suitable for multiple charges of several devices.
• Xiaomi Mi Power Bank 3: Offers a good balance of capacity, portability, and price.
• Goal Zero Sherpa 100AC: Ideal for those needing to charge larger devices like laptops, with AC output and high capacity.
• REMAX Gutitan Series 100W+22.5W PD+QC Outdoor Power Bank with Light 60000mAh RPP-100
  

When purchasing a power bank, consider what devices you need to charge, how frequently you’ll need to charge them, and how important portability is to you. Always check reviews and ratings to ensure reliability and safety.