They are not as powerful for their size, although the best Ni-MH batteries are very close. They used to be more expensive than nickel cadmium batteries, but in the 21st century the cost is similar.
One major breakthrough is the significantly higher energy density of Li-Ion batteries compared to older technologies like Nickel-Cadmium (NiCd) and Nickel-Metal Hydride (NiMH). This allows for ...