Help me understand power banks.

I have (elsewhere) previous been recommended to buy a power bank to uses as an emergency back up for my portable devices.
Which, because I have a candy bar phone with a standby time of 3 weeks, means my tablet and camera.
I was in a shop today, saw one on sale with "for smartphones and tablets" at a reasonable price and bought it
but after I looked at the back it said output 5V 1A.
Oh!
ISTR that when I bought my in-car USB charger I got one for phones and had to take it back and get a higher rated one for Tablets. And even then, one of my tabs reports that it isn't powerful enough to "charge" the device, though experimentation shows that it does keep it operating for a bit longer. Plugging my camera in and it doesn't even notice that there's a charge there.
So I went into all the other shops in the high street to see what they had (lest I should want to take the purchase back whist I was still there) and all of them, with one single exception were output 5V 1A, that exception was fugging expensive and more importantly 3 times the dimensions and 10 times the weight of the one that I had bought. I particularly wanted a small, lightweight, fits in your pocket example.
Back home I looked at my plug in the wall USB chargers, which I (successfully) use interchangeably on all my devices and one says output 5V 2A and the other output 5V 1A.
What's going on here?
what rating do I need to charge my device(s)
I did a quick Google to see if I could find out and found "5 Key Things To Know When Buying A Power Bank" and one of them is "When you buy a portable power bank, make sure that it can charge the battery of a specific device" Yeah, I know that? But how do I find out what that requirement is - I came here expecting that you were going to tell me as the manufactures of these devices keep it as secret as the coca cola recipe (I have been online and downloaded the full specs).
So the item in question is still in its unopened box with all the seals intact (as it's from one of these shops that aren't the best for taking stuff back to). do I take it back and seek out a more powerful one, or open it and try it, and risk the shop refusing my returning it?
tim
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On 04/11/2017 14:50, tim... wrote:

You can't miniaturise the Watt
Bill
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The difference is prices/size is to do with the capacity of the battery, sure
But I'm not bothered by having a power store that will only re-charge my device once, rather than 5 times.
It's the possibility that a low power output doesn't charge it at all, that's the problem
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You need to look, for each device, at the charger you already own for that device. My iPhone charger is a plug with a USB connector plugged into it, giving 1A at 5V. This *should* mean that I can charge the iPhone from any *other* device that I can plug the USB cable into, such as my Mac or my Dell display or even a disk drive with a USB socket. In fact, SWMBO regularly charges up *her* iPhone from her Dell display.
AFAIK, such sockets are rated at 5V, 1A max - that's the spec. This should mean that my iPhone when charging won't draw more than 1A, but I don't know whether devices are clever enough to "try it on", try sucking out more than 1A and look for voltage sag, give up if so.
So if the devices you want to recharge on the go have a charger cable with a USB connector, it should work from any power bank with a USB socket. As you've already noted, the size/cost of the bank just indicates how many recharges you can get from the bank.
That it's rated at 5V 2A won't make your device charge any faster (unless see speculation above). It may allow two devices to be charged at once, instead of one.
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On Sat, 04 Nov 2017 17:05:34 +0100, Tim Streater wrote:

Orginal USB spec is 5 V +/- 0.25 V and 500 mA max.

Depends on the source, is it just a 5 V 1 A "power supply" or is it a 5 V 1 A "USB charger" or a 5 V 1 A "USB port" on a laptop/desktop.
My phone refuses to charge from a "power supply" but is quite happy from a "USB charger" or "USB port". The latter two will have the required resistors that tell the device what charge rate(s) are available. A "USB port" will have the resistors but also monitor the current draw and shut the port down if too much is taken. There may even be a data conversation to agree power requirements rather than just rely on the resistors.
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Dave.
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Certainly the case with my iPhone
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from KT24 in Surrey, England

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charles wrote :

Iphones can be a bit picky about the sources they are charged from, mine is and complains, but still recharges slowly.
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On 04/11/2017 20:25, Harry Bloomfield wrote:

Very slowly. I think that is a standard Apple marketing ploy, IIRC our original iPad was similar.
*Apart* from Apple, I think devices will charge at 1A on a 1A charger, 2A on a 2A one (if they are rated for 2A). Just takes twice as long on the 1A version.
At least we are moving to a civilised world where a high proportion of devices will charge either off 5V from USB, or 12V. And we have the EU to thank for phone chargers.
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On Sat, 04 Nov 2017 17:32:37 +0000 (GMT), charles wrote:

all,

Apple make products that are "fussy" about what they will consider to be a suitable energy source for charging. Various combinations of resistors between the wires an/or ground IIRC.
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On 04/11/2017 21:33, Dave Liquorice wrote:

IME it's the cable more than the charger - very fussy about cables. Anker have been the most consistently reliable non-Apple cables I've used.
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Yep, Apple doesn’t even bother to supply a charger to use in your car and any of them available work fine if you use an official lightning cable. They charge fine from most USB outlets too with the right cable.

And that’s a problem if you want a very short one to use with a power bank or one of those combined power bank cases.

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On 04/11/2017 16:11, tim... wrote:

And I think that can only be answered by you with your devices. I have several portable devices and several chargers. When plugged into a low amp output device one of them reports on the screen "Charging slowly please connect to an approved charger" but does eventually charge. A different device just refuses to charge from the low output device.
Try charging from a standard PC usb output. If its not a USB3 connector then it should be limited to 500mA. If it will charge off that it will probably charge off anything.
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Chris B (News)

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On Saturday, 4 November 2017 15:43:51 UTC, Bill Wright wrote:

I

Meet the pmpo watt, a truly miniature watt.
NT
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On Sat, 04 Nov 2017 09:29:16 -0700, tabbypurr wrote:

But still larger than the Sinclair watt.
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Do all those devices have a 'standard' USB 5v charger as supplied? None of my laptops etc do.
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*OK, who stopped payment on my reality check?

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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London SW

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On Saturday, 4 November 2017 15:52:41 UTC, Dave Plowman (News) wrote:

I thought all laptops came with a charger, thing is they areblt 5V closer to 20V IIRC.
I wonder how long a car would take to charge from a USB port ;-)
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On 06/11/2017 16:23, whisky-dave wrote:

The wife's laptop/tablet charges from USB. Its linx 1010 IIRC.
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On Monday, 6 November 2017 16:43:17 UTC, dennis@home wrote:

The linx is a tablet not a laptop, there's a differnce.
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On 04/11/17 14:50, tim... wrote:

The key figure is the capacity, measured in milliamperehours (mAh), typically on the cheap power banks 1200mAh. It will be stated on the packaging somewhere.
The 5V is the standard voltage for USB and 1A is the maximum rate at which it can charge your phone. So at 2A the phone will be charged in half the time it will take at 1A (assuming the phone can take it which I doubt).
The cheap power banks seldom have the claimed capacity but, for emergency top ups, does it matter that the phone will only be charged to half its maximum?
Another Dave
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