Both NiMh and NiCad self discharge just sitting around, NiMh twice as bad as NiCad. NiCad is more imune to damage due to storage, if you slow charge either NiMh or NiCad for 16 hours at 0.1C and check for capacity. Right off the bat, if any cell did not come up to at least 1.1 volt or higher, it is toast and; if one cell is dead the rest are not far behind. However, it the receiver pack came up to around 5 volts and the transmitter to over 10 volts, then do a discharge test. If either pack does not provide at least 80% of rated capacity in mah when discharged at 0.3C or less, it is time to replace them. As an aside, NiCad are quite a bit better than NiMh in all but 2 catagories. NiMh has more energy storage capability per unit mass than NiCad and are less toxic to the environment when discarded. In all other respects, NiCad rules as they will last twice as many charge/discharge cycles than NiMh, withstand more abuse such as deep discharge or overcharge and have a lower internal impedance. The old myth that NiCad's suffer from a memory is just that, a myth. Both NiMh and NiCad can and do suffer from voltage depression which can often be corrected with a slow charge occasionally, a slow charge being defined as charging at 0.1C for 16 hours. Check out www.rcbatteryclinic.com for some good info on the care of all types of batteries.