NiCad

These batterys discharge after time and have something called 'battery memory' this is where a battery if not kept fully charged will have a tendancy not to hold a full charge.

Suggestions:

Charge the battery fully and then Discharge fully / use till dead

It can be helpful to overcharge (leave on the charge for longer than needed by up to 20%). 

These will reduce battery memory and prolong life. A NiCad battery left discharged will not last as long as a charged battery

Lithium Ion

With these batterys it does not matter from what level they are charged from they will not suffer from a battery memory, however a Lithium Ion battery that is left fully charged will not last as long as an uncharged battery.

Suggestions:

Leave battery fully discharged when it will not be used for a long time.