I can,t charger my dewalt batteries , so is the fault with my charger

It is likely the fault is the battery and not the charger. To confirm this take the charger to any Radio Shack and ask them to test the charger or if you have a small meter do it yourself, the charging voltage will be up to 5 volts more than the rated battery voltage of the drill, so if you get a high reading don't worry about it. Fast charger will be way over the battery rating, also fast chargers have a cost, they shorten battery life due to heat. I have had many battery powered tools, I have found that the batteries last about 2 years on average. I have this same Dewalt drill driver.