Cheap. This charger can be had for $15 to $30 depending on whether you buy it from a dealer or online.
The use of lithium technology in the batteries significantly decreases the weight of these batteries to about half the weight of official Xbox controller batteries. This is great benefit for extended playing time, decreasing hand fatigue and being all around more pleasant to use. Rather then using the ancient Nickel Metal Hydride technology, these batteries utilize lithium polymer.