Hi Morf here. Betsy asked me to jump over here and help with this discussion.
How to decide whether a USB charger is OK to use:
You need to read the small print on the charger. It usually is small print, so if you're an old fa.. person like me, you'll need reading glasses or a magnifying glass!
A bit of background first. The numbers listed will be the Voltage and the Current.
Voltage will be in volts (V). This can either be AC (this symbol ~
), or DC (a little symbol that I can't type - a solid line above a broken line).
Current will be written either in amps (A) or milliamps (mA). A milliamp is a thousandth of an Amp, so 1000mA = 1A, 500mA= 0.5A etc.
With me so far? Ok, let's look at what they mean. The charger will list input and output:
The only thing that really matters on Input is the voltage. This must match the voltage and AC/DC of your supply.
US Mains is 110V AC.
UK/Europe Mains is 240V AC.
A car is 12V DC.
[For AC, the frequency is also relevant -50Hz or 60Hz - but if the charger matches your voltage it will almost definitely match your frequency.]
This is the important bit.
Firstly, look at the voltage. It should be 5V DC or sometimes 5.5V DC. If it's any more or less than that, do not use it
. You may cause irreparable damage to your Kindle.
Secondly, look at the current.
current should be is 500mA (0.5A).
All Kindle devices are designed to charge from a PC USB plug, which supplies 500mA. As long as your charger supplies at least this, it will work fine.
Some phone chargers are less than 500mA (I've seen 400mA). If you use one of these, you may damage the charger.
current? There isn't one. Your Kindle will only use as much current as it wants.
Be aware, though, that depending upon your Kindle model, it may take a long time to charge if the current is only 500mA. Amazon state http://www.amazon.co.uk/gp/help/customer/display.html?ie=UTF8&nodeId=201002760
that a Kindle Fire will take over 10 hours to charge from a 500mA supply, whereas it will charge in 3.6 hours from it's preferred charger (which I believe is 1.8A).
If you are using the Fire while it is charging, you may find that a 500mA charger is not enough to keep up, ie the battery will slowly discharge or stay at the same charge level.
High current chargers will charge faster, but only to a certain extent. A standard e-Ink Kindle's maximum current draw is about 800mA. For a Fire, if you want to use it at the same time as charging it, it can draw up to 1.3A or more. A higher charger current than the standard charger (850mA for e-Ink, 1.8A for Fire) will not charge any faster than standard.