Charge it again the night before.

Memory problems are a thing of the past (or of myth, depends on who you talk to). In any event, you don't have to sweat battery memory with modern Nicads. And certainly not from what you describe.

I don't have hard numbers on the % charge loss over time, and I'm pretty sure it varies a bit depending on the make and size of cell. But why not play it safe, and put the thing on charge the night before.

At the very least, put a meter on it, and see if it's holding above 4.8v.