The key is to match your cell phone's charging standard when it comes to portables for cell phone charging. Most of the modern iPhones, as well as the majority of the Android phones charge via USB-C, which is why the power bank with a USB-C Power Delivery port will suffice. The difference is that this is VERY quick. Many Android phones can come in with faster protocols like PPS, and the iPhones fast charge with regular Power Delivery, which means a bank that provides both protocols will offer the fastest speeds on both types of phone. You should check your phone's maximum charging wattage and select a bank with at least that level, since a more powerful bank cannot "overcharge" your phone.Wireless is the other choice. Some Android phones also have magnetic charging which will snap onto the base and charge the phone without any cables.Mobile phone magnetic charging is supported by new iPhones, and some Android phones as well, allowing a magnetic portable charger for mobile phones to be snapped on and charged without the use of a cable. It looks pretty cool, but it does not charge as fast as a wired charger; it's hot to walk on, and can empty the battery bank very quickly, so I also have a wired charger just in case.5000mAh about one charge, 10,000mah about one and a half to two charges and 20000mah for multi day trips. Also, weight and thickness play a factor; if it doesn't fit in your pocket or small bag, then you're not going to be carrying it! A few habits help. Make sure you use the cable that came with your phone, or a verified cable, do not charge in hot places such as a car dashboard and let the bank charge from a proper wall adapter. Use as handbag when traveling by air.If you need help with something in particular, techyassist is a good place to look, as they provide honest reviews of gadgets and carry them with them to see if they can be helpful. Select an appropriate charger for your cell phone and dead batteries are no more a cause for concern.