This has been an issue that's been bugging me the last few days now. The stock wall charger that came with my Droid X is the 5PN5504A, which has an output rating of 5.1V, 850mA. My understanding is that the mini-USB interface is an industry standard for power delivery to portable devices, which I take to mean that any charge source should work (wall charger, desktop PC, laptop) as long it has uses an USB interface. So any USB-->miniUSB cable can be used to charge any mini-usb device, regardless of power source, right? I already have several other mini-usb devices, such as bluetooth headsets, which all came with their own wall chargers. However, I checked these chargers, and they all have different outputs: 5V @ 200mA, 5V @ 150mA, 5V @ 550mA. Because the default Droid X cable was so short, I was tempted to use these other chargers. I plugged in the 5V@150mA charger to my Droid X, and found that the phone does not show it's charging (the lighting bolt isn't there, there's no animation on the battery indicator). So then I switched to the 5V@550mA charger, and it DOES charge. I guess this means is that certain devices have a minimum charge current at which they will charge. So my worry is, is there a MAX charge current as well? I understand that using a higher current will charge the battery faster, but if I use a charge source the provides more than this safe max amount, will it fry the battery or shorten it's lifespan? I recall from prior research that each USB port in a PCs provide 500mA, but how do I interpret this? - Does the port provide constant 500mA to the connected device? - Does the port provide a maximum 500mA to the device, but varies depending on how much the the device needs - Is there any harm if I charge my bluetooth headsets using the PC USB port? (the one that comes with 5V @ 150mA charger) - Do smaller laptops (netbooks) USB ports deliver less current than PC USB ports? Any advice or illumination would be highly appreciated, whether specific to the Droid X or mini-usb devices in general.