NiCD (Nickel-Cadmium) and NiMH (Nickel-Metal Hydride) are two very different types of batteries. Both types must be handled differently from one another in regards to charging and discharging procedures and philosophies.
In general, NiMH batteries cannot handle the high rate of charges or discharges (typically over 1.5-2 amps) that NiCAD batteries can. Many modelers use high rate, peak detection or time-based chargers to charge NiCAD batteries. Such chargers are NOT recommended for NiMH batteries (unless otherwise specified in the charger or battery literature) as they can cause permanent damage to the NiMH cells. Also, NiMH batteries will not perform well in high rate discharge applications, typically providing only a small fraction of the rated capacity in these instances.
NiMH batteries also have approximately twice the self-discharge rate of NiCAD batteries when in an used state. For example, when your radio is off, a 1650mah NiMH battery can discharge itself nearly twice as quickly as a NiCAD battery, typically within one week. Therefore, you must charge your NiMH batteries the night before each use.
When handled correctly though, NIMH batteries can be very beneficial, providing much longer run times than comparably sized and weighted NiCAD batteries.
We highly recommend NiMH batteries in applications that call for long duration but not a high amp load. If you have an aircraft with very large servos that pull a lot of amps or more than 8 standard servos we recommend using NiCAD batteries for the best results.
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