I haven't seen the instructions for one of these but on general principles - NiCad/NiMH chargers are generally current limited to suit the capacity of the battery being charged. As long as they give out more volts than the fully charged pack, they will offer the limited current, whatever the configuration of the battery. If it is capable of putting out 24 volts, it won't care whether it is charging 1 cell or 10, it will just give whatever it is set for, and will probably do so until it is disconnected. Fast charging is another story.
NiCad/NiMH don't really care what voltage is used to charge them, BUT they are picky about the current being shoved through them, so their chargers need to be current limited, as opposed to SLA where they do need something to limit the voltage as well. Or Lithium types where asbestos gloves and a magic wand and a concrete shed at the end of the garden are useful.