Per some of the info printed on the back of all Kindle readers the maximum charge voltage and current is listed. All I have except the latest PW4 and Oasis G9 and G10 list maximum input as 5.2V and 500 mA. The current PW4 lists a max charge rate as 1000 mA and both the Oasis G9 and G10 list a maximum charge current of 1500 mA at the same 5.2V max. Many older computers with USB2 ports are limited to the 500 mA output and the Amazon basic charger is 5 watts or 1000 mA output. Overpriced IMO as is the Amazon similar 9 watt wall wart charger. In comparison some of the latest Apple devices, and others, have charge rates of up to 90 watts with USB 3 ports.
The PW4 and Oasis 7" models should charge considerably faster than older models if a modern USB charger with at least 7.5 watts power output is used along with a heavy duty USB 2 cable. The reader's internal charging controller actually controls charge rate so a USB charger or battery pack with greater current output capability will not damage the reader. Otherwise I would have fried all my readers long ago.
