In general, follow the device manufacturers guidelines for battery selection which can be found in the operating instructions. First of all, you should not use a NiCd charger for a sealed lead acid battery and vice-versa. Each chemistry has specific charging rates and characteristics that cannot be interchanged. Early designs of NiCd batteries with primitive electrode technologies had problems when the batteries would be charged at exactly the same time each day. Voltage Depression, mentioned above, is the most common problem associated today with NiCd's.
Voltage Depression occurs when batteries are overcharged for extended periods of time.
When this happens a voltage depression appears at the end of the discharge curve. As prolonged overcharging continues, charge temperatures are elevated, and this depression slowly progresses to the mid-point of the discharge curve. This results in loss of the usable capacity or run time of the battery. Voltage depression can be reversed by conditioning the battery. This involves discharging the battery to 1.0 volts per cell and then recharged.