///Edit 25/3 First review is up./// Hello everyone! A bit of background... As a gadget fanatic and tech lover, I was seeing too many misconceptions about portable chargers/power banks and everything related to the topic, that at one point I decided to make a forum thread about it, to hopefully be able to help those people to clarify all doubts about related to these devices. I have the right equipment and a massive amount of portable chargers of all brands and capacity, but in this case I will test only those that can be bought by most. To understand how the charging process works, we must first understand the basics: we have Volts, Amps, and Watts. A neat analogy to help understand these terms is a system of plumbing pipes. The voltage is equivalent to the water pressure, the current is equivalent to the flow rate, and the wattage is the total amount of water that have flown through it. Common Misconceptions: 1. Since my power bank says 15,000mah capacity, it should recharge my iPhone 5 10x times since it has a 1,500mah battery. False. The said capacity on a any given portable charger, represents only a roughly estimated capacity of the internal battery. This internal battery has a nominal voltage of 3.7v, but your iPhone/iPad requires 5v to charge, so the internal circuity of your portable charger starts to do the step-up conversion, and since no circuit has a perfect efficiency level, some of the power is lost, which is about ~15%. So that means the capacity is 12,750mah? Not really. Remember when we said that the iPhone requires 5v to charge, but the battery is only 3.7v? when the power reaches your device, it then starts another conversion, this time a step-down, and this also means a certain quantity of lost energy. It is really difficult to say how much, but let's suppose another 10%. After all the loss during the conversion, we could say the 15,000mah battery pack roughly puts out 11,000mah into the device. So in the best case scenario, it will fully charge your device about 6-7 times. The detailed math is actually more complicated and involves watts, which is the precise way to measure power, and basically goes like this: Watt is the unit for Power, which is the result of simply multiplying the Current by the Voltage. It usually involved times, to accurately measure how much power has flown over certain time (1 Hour) -----Quick example------ An iPhone charging at a rate of 1A @ 5V, (5Watts) will take about 1h40m, requering aproximately 7Watts to fully charge it, while the internal battery is only rated 5.5watts. A external battery with a 3.7v battery and rated capacity of 10,000mAh, after roughly ~25% overall efficiency loss: 3.7v x 10,000mAh= 37,000mWh - 25% = 27,750mWh. 27,000 / 7,000 = 4. So technically, under good circumstances a 10,000mAh rated external battery can fully charge an iPhone 5S 4 times. ----- Also be aware that most products have an overrated capacity, for.... you know... marketing purposes. Most portable chargers in the market as of now use type 18650 Lithium-Ion. They are proven safe, compact and cheap to produce and are basically the same as the one in your phone, just rolled into cylindrical shape. So have you wondered, why do manufacturers rate their power packs with such strange capacities, e.g. 2600, 5600, 10400, 15600mah? This is because 18650 batteries comes in standard capacities, and they go from 1,200 to up to 3,400mah, with 200mah steps. Their price increments gradually as the capacity increases, and they can vary A LOT depending on the quality of the cells. In a 10400 rated pack, the manufacturer uses (or wants you to think it does) 4x 2600mah cells. But even when you pop it open, there is no exact way to visually identify the capacity of said battery, if there is no spec on it: This is a chinese power bank with 4x parallel connected generic 18650 cells in it, they are probably rated 2,400 but actual capacity could be as low as 1,400mAh. Avoid them. But there are times where genuine branded batteries are used, like this samsung 18650 cell, rated 2,600mAh, which I was very happy to find inside the RavPower 10400mAh: (Not my picture, but this is how it looks like) I would seriously reconsider the recommendations by those reviewers who without actually properly testing the portable charger, submits a 5 star reviews of the product, along with a wrong math of how many times said battery pack SHOULD charge their phones. Once I got one based on one of these reviews (Incredicharge I-11000). I still regret it sometimes. 2. I have bought a wall charger/car charger/portable charger that puts out 2.1A instead of 1.0A. It should charge my iPhone at double the speed. False. After testing with all sorts of chargers and brands, I was surprised that the iPhone 5S will always limit the charging current to 1A. which at 5 Volts, makes a power input of 5 watts. I have seen numerous "experts" reviews where they assure their phone charges much quicker when paired with the "12 watts rapid charger". Worse yet, many people make the wrong purchase based on this information. (even though it would work and won't damage your device). My iPad on the other hand, will gladly take 2.1A. The only real advantage of buying a 2.1A charger for your iPhone is that because the charger is just working half capacity, it does not get as hot and probably last longer. On a real world test, my iPhone 5S would charge almost exactly 1% per minute while not in use. 1% of charge per minute is what I consider a full 1A output, and anything that can do this rate without heating my device is worth keeping. Start your timer and set for 20minutes, when it's done, your iPhone should have charge AT LEAST 18%. Try it yourself! Many of the chargers that supposedly would put out 2.1A will not even come close to it. This results in a slow charge, but there is a way to know whether if your charger or cable is worth keeping or not. Google "USB Power Meter" and you shall find plenty. It has an usb input and an output, measures the Current (Amps) and Voltage that goes through it. They cost around $10, and you will be asking yourself why you didn't got one of these earlier. Example of a chargers you should avoid: Please stay away from this one at all costs. This is a generic car usb charger, it has been around for years, but sadly still in production and on sale in many many countries. It only puts out 450mA, if you are lucky. I believe having seeing them in CVS or Walgreens for $10. Poor folks who have bought them. I would also avoid these generic kind of All-In-One multi-port charger, as they tend to divide the overall current between the connected devices. You would charge more devices, but at the expense of taking the same or even longer than charging them individually. 3. Cable quality can affect charge rate. They do!! I have tried several lightning cables, and some of them would limit the charge rate from 2A to barely 1.4A when charging an iPad. There seems to be due to a weak cable, or low quality lighting connection chip, or both. I personally recommend only the genuine apple cable, as it has proven to be the MOST reliable of them all. (belking, griffin, truewire, you name it.) Some people complain about the quality of the apple cable, but come on, the first cable that came with my iPhone 5 about 2 years ago still works perfectly, while my Belkin branded cable broke near the connector, revealing non shielded internals! Amazonbasics cable is pretty good as well. This is how a shielded Apple cable looks like. I really hope this information has been useful to you. Soon I will be refreshing this thread with the first detailed review and the equipment used to measure. Thanks for reading!