Extremely useful!
This is a great item to get if you're going on long car/airplane trips, and don't have access to a power outlet.

3 AA batteries will get another 4 hours of gameplay, and even more hours of sleep time!

Important Fact
This item is really good for extending the battery life for your DS in long trips especially when you're on an airplane for numerous of hours with no electrical outlets available, but one important thing that everyone should know is DO NOT use the wireless function while on an airplane (it will interfere with the airplane's radar - same with cell phones).

Great alternative to AC adapter when needed
Perfect for long trips on an airplane or long days in school when you may not have access to an electrical outlet and/or your A/C adapter. This product is very lightweight and smaller than I expected. It takes 3 AA batteries which pop in the bottom compartment with no problems. The unit has an on/off switch so you can keep the batteries stored in the Charge Boy when not in use by simply turning off the power switch. The Charge Boy has a cord (approx. 2 feet long) which is plugged into the power slot on the DS (the same slot you use to plug in your AC adapter). Turn on the switch and a glowing orange light on the Charge Boy signals that the DS is charging. When charging is completed, the Charge Boy blinks with an orange light. You can then turn off your Charge Boy and disconnect the cable. The Charge Boy has some nice cable management features - 2 slots on the Charge Boy to wrap up the cable and one on the cable to tie it down.

You can also plug the Charge Boy into your DS while you are playing your DS to extend the battery life on your DS. I was on an airplane a month or so ago and my DS battery died, so I had no chance to recharge the battery until we landed and found an outlet in the airport terminal. Now I can just plug in the Charge Boy when the DS battery dies and keep on playing for up to four more hours. If I bring 3 spare AA batteries on board, I can extend my playing time for another four hours after the first set of AA batteries die.

Basically, this unit makes your DS capable of running on regular alkaline batteries, just like the GBA. It also works as a charger for your DS as an alternate to an AC charge. Not what you would want to do on a regular basis, but perfect when no electrical source is available and it works great.