If you have wireless controllers for your Xbox 360, this is a must buy. The kit comprises a charger, mains cable and one rechargeable battery pack.
The charger can take two battery packs at any one time and will charge both in around four hours, or a single battery in about two hours. The battery pack lasts ages in your controller so charges shouldn't be too frequent. There are status lights on the front indicating if the batteries are still charging or have finished.
There is also a separate Play & Charge Kit for the 360, which plugs your controller into the console's USB port to charge the battery. All well and good, but it doesn't charge as quickly and the cable defeats the object of having a wireless pad. For these reasons, the Quick Charge Kit is a better bet.
Extra battery packs cost about £9-10 and are worth the investment. The whole set-up will pay for itself within a matter of weeks compared to the equivalent cost in AA alkaline batteries, so get one today!