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. Becuase 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? And if there is a safe range of charge currents, then what exactly is the output voltage when I'm charging the Droid X using laptop or PC USB ports? Or does the output current from PC USB ports vary depending on the draw of the device? Any advice or illumination would be highly appreciated, whether specific to the Droid X or mini-usb devices in general.