The Console
The most obvious way to charge a PlayStation 3 controller is to plug it directly into the console itself using the USB cord. While the controller is charging, you can still use it to play video games, surf the web, watch videos and more. However, you cannot charge the controller while the PS3 console is either turned off or in sleep mode. The controller can be charged on any PS3 console. Once it's fully charged, a solid red light will appear. If the controller needs to be charged, four flashing red lights will appear. If you are playing a game and your controller is losing power, text will appear on screen indicating such.
Another Source
John P. Falcone wrote an article in October of 2008 for Cnet.com explaining different ways of charging a PS3 controller. Falcone states that you can charge a PS3 controller by plugging it into the USB port on your PC, or you can connect it to a satellite box such as a DirectTV HR20 or a Dish ViP622. Using an iPod AC adapter or any other form of USB charger did not yield positive results according to Cnet.com. You can also charge a PS3 controller using the USB ports on a laptop computer.
The Charger
You can purchase charging devices for your PS3 controller such as the Energizer Power and Play Charging System. This device allows you to charge up to four controllers at the same time. Two controllers can be charged on the actual charging station, and two more can be charged using USB cables plugged into the station. The main benefit of a charging station is that you don't have to have your PS3 console on to charge a controller.
Warning
The rechargeable battery within the PS3 controller is locked inside, meaning you cannot remove or replace it. If the battery eventually dies, you will have to purchase a new controller, so turn your PS3 console off when it's not in use. Once the console is off, the PS3 controller will automatically turn off as well.