The first thing to consider when buying a portable charger is the amount of power it has, but you should not just simply take the numbers on the box. Usable capacity is approximately 60 to 70 percent of the stated capacity and will typically charge a conventional cell phone about two times. This is due to some loss of energy when converting the voltage, so don't overestimate the capacity. 10,000mAh is fine for everyday use and 20,000mAh will be good for longer journeys or anyone charging their phone, ear buds, and tablet.Then check out charging speed and charging ports. Anything that has USB-C with Power Delivery is a modern portable charger, and that's what fast charges recent iPhones and Android phones, and even high powered small portable laptops. Look at the output watts and remember, the phone and cable need to support the speed as well. Magnetic wireless like Qi2 for the newer iPhones can be convenient for occasional use, but they charge slower than a cable and are hotter in use, so I still like to use a cable for a quick charge.Safety is more important than it seems. Pick one from a well-known brand that specifies protection against overcharging, overheating and short circuits and do not use the cheaper brands that boast of "a very high capacity" without being more specific. If you are flying, power banks are required to be in your carry-on case (not checked luggage), and most airlines have a limit of 100Wh or approximately 27,000mAh without special permission (but some airlines have now restricted the use of power banks during the flight, so check with your airline).However, if you prefer to read real reviews over marketing pages, TECHYASSIST is worth a visit as they write honest reviews, and the devices are always sold on the same website. Regardless of the model, a portable charger you buy should be as much as your personal phone usage and travel frequency.