If you use a charger which is compatible with Apple products, it will cause the vbus_present wakelock since Apple does not adhere to USB standards and requires two of the pins to be bridged or open (can't remember which) to work for their products. However, when you charge a device that does adhere to USB standards with one of these chargers, it will cause the wakelock (on all the samsung phones I have seen, anyway). Another downside to using an apple compatible charger is that you can never get more than 500ma out of it due to the non-standard USB connection, even if the charger is capable of 2000ma output. So you get slower charging. When you are connected to any charger, this wakelock will be present. If you use an Apple compatible charger, it will persist after you unplug it and will drain your battery around 10% per hour since it prevents it from going into deep sleep. You can clear the wakelock by rebooting the phone or plugging it into a standard USB charger, such as a PC or Samsung charger, even for a few seconds. You can use Better Battery Stats to see the effects of this wakelock. Note that it can take a few minutes to show up once you have unplugged from the apple charger.