Portable Chargers: what you need to know, + Review thread

Discussion in 'iPhone Accessories' started by TEHi, Mar 23, 2014.

  1. TEHi, Mar 23, 2014
    Last edited: Mar 24, 2014

    TEHi macrumors regular

    Jan 6, 2011
    ///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.

    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". :mad: 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!
  2. Zmanbaseball2, Mar 24, 2014
    Last edited: Aug 1, 2014

    Zmanbaseball2 macrumors 68040


    Aug 24, 2012
    New York, USA
    Portable Chargers: what you need to know, + Review thread

    I find that this thread was needed. I do have some reviews of usb power meters if you want me to post them:)
    I'm a reviewer. I understand that around 20-30% is lost so I do the math:)
  3. SaintsMac macrumors 6502a

    Jun 13, 2009
  4. TEHi thread starter macrumors regular

    Jan 6, 2011
    First review is up!

    I will start with the Sony CP-F2L. It has been one year since I got it, and although it is not longer the one with most capacity nor the fastest charging, it is and will remain as one of my favorite because it is just so reliable and well built.

    The sony CF-F2L is rated 7,000mAh, with 2 USB ports and an on-off button. Inside the aluminium body, there are 2 flat type Li-Ion battery, 3,500 each in parallel setup. What makes this external battery so good is its simplicity, one click turns it on, and it will flash 1-3 times depending on the battery level, and then another click turns it off, or it automatically turns off when the device is fully charged. Most Sony products are well engineered and this one is no exception, it feels really solid in your hand and has taken a couple drops as well, but has never failed to work while it holds a charge.

    I have never seen such detailed info on any charger, and I don't think I will ever do. It is clearly detailed that output is 5V, at 2.1A max, and with a capacity of 4,700mAh it will put out a total of 25Wh, and this is achieved by using 2x 3,500mAh batteries.

    At first it may look confusing, 7,000 to 4,700mAh is a huge drop, but actually it is pretty self explaining:

    Battery capacity:
    7,000mAh x 3.7v = Battery holds 25.9Wh of power.

    Output capacity:
    4,700mAh x 5v = At 5v it will deliver 4,700mAh, 23.5Wh

    25.9Wh to 23.5Wh means a mere 10% efficiency loss, which is quite good.

    Real world test:

    I have been using this power pack for more than a year and I really never accurately tested it until now. All I knew is that it could charge my phone a couple times, but exactly how much power does it deliver?

    The equipment and method:
    There are many ways and devices and can measure the volts, amps, power, and capacity, they can vary from $5 to up to thousands of dollars. The one I found most capable of measuring every factor in what comes to usb charging, is the Portapow premium USB power monitor. It costs about $40, has a large LCD screen and most importantly an internal battery. Why? Because this way even if the battery pack is depleted, it will still show the measured data instead of just turning off, and secondly it draws no power and means near zero resistance into the charge. Simply connect one for input and the other for output.

    When paired with an iPhone 5S, you can see the voltage is a bit over 5.1v which means a healthy charge, when the voltage drops it means that the charger is not able to keep up with the output, and this will result in an improper charge and even overheating your device. Amp draw is almost 1A, which in this case is limited my the iPhone itself. Maximum Ampere from this charger is about 1.03Amp from each of it's ports, totaling 2.1A as stated. I would not recommend using this for an iPad.

    The portapow power meter had two display modes:
    First one displays output capacity in real time (as seen above, it shows Watts and the total mAh that has been delivered to the device). This data is not very relevant.
    Second mode however is what I bought it for. It will show the elapsed time from the second the charge started, and the total amount of power in Watts that has been delivered to the device. See image below:

    Oh and it has backlight too.

    After a round of full discharge by using a USB flashlight that draws 0.8A steady@5v, the Sony scored 20Watts. It falls short of the 25W printed on the back, and this might be related to battery wear over time and usage.

    An iPhone 5S will use 7.8Watts of power to charge from 1% to 100%. So simply put, it will be able to charge it 2 and a half times. This is more or less what I get in real usage.

    Bottom line:
    What you must really consider in this kind of tests, is not the pretty and big number on the product description, as the seller or manufacturer wants you to think, but the amount of POWER can it can deliver. Sadly, 99% of the people just tend to go for the one with a larger mAh rating.

    Here is another simple analogy that will help explain better:

    You have a jar of water that you should use to fill a few cups. volt and amp only means the size of the jar and how quickly you can pour it into the cups, but watts is what defines how much water you actually have to fill them.

    Let's say if you have a Battery pack that delivers 78watts, it will charge your 5S 10 times, PERIOD. No matter what mAh rating is has, at the end what really matters is the efficiency of the charge, otherwise all that energy just goes to waste.

    I hope I have covered the main points of what you should consider in your next buy, if you have any question please feel free to ask!! :)


    Of course!! thank for contributing!!:D
  5. Zmanbaseball2 macrumors 68040


    Aug 24, 2012
    New York, USA
    The Centech USB Power Meter is a great tool for measuring voltage and amperage of USB power.

    -Very small in size and has a clear enclosure so the internals are visible
    -Display that gives the amp/volt readings and the peak of each reading in a different mode (4 modes)
    -Readings update every second
    -Accurate readings (I have a different brand USB meter and it has the same reading)
    -Can read 0-2 amps and 3-6 volts with accuracy within 0.04A and 0.05V
    -USB pass-through for a PC (can use a thumb drive that is plugged into the meter and that is plugged into the PC and the PC recognizes it)
    -Works well for testing the output of battery packs, wall chargers, car chargers, and ect that is plugged into a device like an iPad
    -Great tool for reviewers, like me, who want to know how the product performed in real world tests
    -Great quality

    -Takes 4 seconds to turn on (others turn on instantly)
    -Need light to read the screen
    -Only reads up to 2 amps (iPads can charge up to 2.4 amps and others I have go up to 3 amps)
    -More expensive than others on Amazon

    Note: The device connected needs to at least draw 0.05A of power for a reading.

    This is a great USB power meter and I recommend it.

    USB Power Meter by Centech http://www.amazon.com/dp/B00DAR4ITE/ref=cm_sw_r_udp_awd_Bmtmtb1AYFVKX
  6. B2FiNiTY macrumors member

    Nov 28, 2011
    Great review.

    I've worked in manufacturing for a lot of those chinese companies that make the "power banks" and you're right, gotta stay away from the low end. There is a high chance they will fry your device. :eek:
  7. Zmanbaseball2 macrumors 68040


    Aug 24, 2012
    New York, USA

    I can add over 50 review to this thread. I'm a reviewer and have so many battery packs.
  8. TEHi thread starter macrumors regular

    Jan 6, 2011
    I believe this forum should have a sticky for this topic, so all reviews and inquiries can be found under one place. Sadly most of my power banks cannot be bought in the US, so it would be pointless reviewing them.

    Do you have a website? and which models have you reviewed before?
  9. Zmanbaseball2 macrumors 68040


    Aug 24, 2012
    New York, USA
  10. 10-Dee-Q macrumors 6502

    May 10, 2006
    Bandung, West Java, Indonesia & Singapore

    I have this exact sony portable battery
    And i've been very happy with it so far
    I used it most of the time for my 5s and 4s but sometimes i do use it for my ipad air.
    Btw can you cslculate "how much" this portable battery could chaarge a totally depleted ipad air? Thank you.
  11. Zmanbaseball2, Mar 26, 2014
    Last edited: Mar 26, 2014

    Zmanbaseball2 macrumors 68040


    Aug 24, 2012
    New York, USA
    Portable Chargers: what you need to know, + Review thread

    I think around half. 7000mah minus 30% is 4900mah an iPad Air has an 8820mah battery. It will charge it about half I think again depending on how much you use the battery pack. If you want a full charge you need at battery pack that has an 10000-11000mah+ battery pack that has less than a 20% power loss.
    Like these:
    [Upgraded Version & All Smart Ports] Anker® 2nd Gen Astro3 12000mAh... http://www.amazon.com/dp/B00CEZBKTO/ref=cm_sw_r_udp_awd_NoWmtb07AS7SN
    New Trent PowerPak Xtreme 12000mAh Rugged Water/Dirt/Shockproof Dua... http://www.amazon.com/dp/B00HCMZUZE/ref=cm_sw_r_udp_awd_IpWmtb14X7ZQ9
    I have both of them and they work great.
  12. macher, Aug 1, 2014
    Last edited: Aug 1, 2014

    macher macrumors 65816


    Oct 13, 2012
    OK I have questions. Would like a more layman's explanation, not as technical.

    This is what I know from doing research. But would like explanations for a regular Joe like myself. You're explanations although excellent, as a regular Joe I can't understand.

    This what I have found so far...

    Manufacturers are only required to label 'raw' mAh not the net mAh. So an advertised 9,000mAh power bank isn't really the true capacity. BUT if we are going to find out how well a power bank can charge your iPhone according to advertised mAh do we take the mAh of the power bank/the mAh of the device? In this case 9,000mAh power bank/1,440mAh iPhone 5 battery= 6.25. So an advertised 9,000mAh power bank IN Theory should be able to charge an iPhone 5 from almost dead to 100% 6.25 times?

    From doing research I think we have to take into account not the labeled mAh but other factors like efficiency rate but I don't know what this is and how it plays into getting the true capacity of a power bank. Some power banks boast a 20% efficiency rate whatever that is. So I'm thinking the 9,000mAh power bank in my above example won't really charge an iPhone5 6.25 times.

    Can you elaborate so a layman like myself can understand. All I know is capacity of the power bank, amps of the charging ports plays and important factor in getting the best power bank but don't know the details.

    What are the main factors or terms a common consumer should know when searching for a power bank?

    Is my list correct?

    Capacity(mAh), and how to determine the true mAh. The advertised mAh isn't the true net mAh.
    Ports, what kind of ports do you need to charge an iPhone or a tablet and why?


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