Please look on your drill and post the Model #. DeWalt tools have a one year warranty, batteries if they have yellow top have a 2 yr. warranty. There are manufacturers date codes on both, this tells you when the tool/batteries were made. A DeWalt service center can help you. All batteries have so many charge cycles. It may be your batteries have used almost of these cycles, therefore they don't take and hold a charge very well.
Your drill may also need new brushes, sometimes the tool will drain batteries quickly.
Unlike many other tool brands, DeWalt has the most consistent use of batteries/chargers & tools on the market. Milwaukee is getting into trouble with those having Milwaukee cordless because they are changing batteries and chargers so often and they do not interchange.
Thus you have different Milwaukee cordless tools that may take a totally different battery and charger than what you have.
DeWalt's new Lithium Ion batteries interchange in the current NiCad tools so you are not forced to switch.
DeWalt spends more time/money on engineering new tools which means they take more time in designing and engineering their tools but when they are introduced they are full of the newest technology available.