How to fix cordless drill batteries?

I have a 18v cordless drill (not sure of make)the battery has a small monitor button on side which lights up 4 small lihghts when pressed,to let me know how much life is in it, it only two lights appear,and it holds very little charge,is there anything I can do,! to resusitate this battery in any way it is a ni-cd 18v 5hr charge,any info' would be much appreciated,many thanks.