Lithium Ions in drill drivers are a fairly recent phenomenon. Like in the last 18 months. Anything before that was likely a nicad battery. NiCads do develop a charging memory and it is preferable to use them till "empty" and then do a recharge. Otherwise after several half cycles, half empty will become the new empty. Hence the term, charging memory.

Lithium Ion batteries do not have this issue. You can recharge them any time from anyplace in the cycle without worry of developing a memory. Though, it is preferable to "deep discharge" them periodically.