I have a 24V lithium-ion combo kit that I really love, but I'm needing an extra battery or two, and the 24V lithium-ion batteries are just too expensive. I tried a 18V nicad battery in my drill and it seemed to work fine, and the repair man that I talked to told me that as long as the battery fits in my tool, it should be just fine. I just want to make sure that putting a lower voltage battery in my tools want hurt the motor or mess up anything else. So if anybody has any nuggets of wisdom, I would greatly appreciate any advice and/or feedback. Thanks!