Nickel-metal-hydride batteries are a newer battery type than nickel-cadmium. They have a higher energy capacity than nicad, but have a much shorter life (about 100 charge/discharge cycles), and they are more easily damaged by overcharging and vibration.
NiMH batteries can be charged at a maximum rate of 1C, however, some people claim the Sanyo HR2600SC can be charged at 2C rates. This warms up the cell for maximum performance prior to flying. Chargers will fail to properly terminate the charge when NiMH cells are charged at rates less than 0.4C, so slow charges must be carefully timed to avoid overcharging the cells.
NiMH batteries can be left either charged or discharged at the end of a flying day. When stored long-term they should be stored in a cool storage area. After storage, they should be cycled a few times to restore capacity.