Normal room temperature Ryobi BCL14181H not charging NiCad 18V completely. Charges for approx 15-20 mins then goes to steady green as if charged. If battery removed and replaced, the charging continues for approx 15 mins It takes 3 or 4 re plugging in to obtain full charge. This happens with all my four 18v NiCADs. Li ion 4ah batteries charge ok. Exchanged the charger and the same thing happens with the replacement unit. The NiCADs charge OK on the original charger supplied. Can you advise please? Regards, John