Are you talking about a battery charger that came with the cordless drill? If so, why wouldn't you just plug it in? I think most all devices that are sold with chargers turn off the charging when done.

You would need to know the total amp-hour rating of the battery pack. For example if it was 1 AH (= 1000 mAH), at 350 mA it would take about 3 hours minimum.

I lost original charger. I dug up another. I did find online manual and it says initial charge should be 18hrs. This drill/charger is old tech. 10yrs old. Certainly not automatic charging capable.