On 04/11/2017 16:23, tim... wrote:


"Another Dave" wrote in message
news
On 04/11/17 14:50, tim... wrote:
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.


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.

I understand that, it is 2000, the expensive one was 10,000 - enough to
recharge a device 4 or 5 times.Â* But I don't need that.

I'm not concerned by the battery capacity, it's the output current
that's the issue here.


That would only matter if you wanted a faster charge - is that what
you're after? If so, yes, you're right, higher current. But IME it
doesn't always work that way - some devices seem to 'choke' the input.

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 devices are tablets, some of them (apparently) wont charge at 1A.


I've not heard of that. My iPad charges fine (if slowly) from a 1A
charger. I can't explain why you had issues with the car charger.

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 less than its maximum?

Nope, not a problem, as long as it works I don't care how inefficient it
is. I really am only going to use this as an emergency back up whilst
out during the day, not as a strategy to avoid plugging my tablet in
every evening at the hotel (or at a location where I'm not staying in a
hotel).

I am only concerned that it may not work at all.


It should work. Could you try with a 1A mains charger?


--
Cheers, Rob