Good Morning,
It's important to be cautious when handling Ni-Cd batteries. If the batteries are old, they may have lost capacity or even leaked, so inspect them for any damage. If they're still in good condition, you can try charging them with a compatible charger, but make sure to avoid overcharging, as Ni-Cd batteries can be sensitive to that.
It's good practice to fully discharge them before recharging for maintenance to avoid the memory effect. So, store unused batteries in a cool, dry place to prolong their life. If you're unsure about the condition of the batteries, it might be safer to dispose of them properly and consider replacing them with new ones.
I hope this helps!