Sanyo offers enhances batteries with their Eneloop line, something that can reportedly last for as long as five years. Apparently, unused fully charged Eneloop batteries retain 70% of their capacity even when unused for the said 5 year period.
Actually the useful life varies. If unused just for a year, it only loses 10% of its charge. The new and improved batteries should be a big boost, especially in cases of emergencies such as the devastation that hit Japan. About 1,800 times, a 20% increase over the previous generation. They also come fully charged from the factory, exclusively with solar power, so they can be used straight out of the package.
The new Eneloop batteries are scheduled to be available this November.