Having experienced a similar issue with a DeWalt battery, I can offer my experience. All these batteries are made up of a number of small batteries (in my case, 17) similar to a stubby version of an AA battery in shape. They are all soldered together in a cascade using thin foil rather than wire.
Sometimes one of these foils break, breaking the circuit and you can repair the battery by replacing the foil with suitable wire.
However, if you can open the battery and find everything intact, it means that one or more of the cells is internally faulty. Unfortunately, the cells are not replaceable.
You could in theory unsolder each of the cells to test them for voltage on a multimeter, remove the faulty cell and reconnect the batteries. However, there's no guarantee the cells would provide enough voltage for your drill to work.