absolutely
1, 18V and 21V battery packs are 5 lithium batteries in series, but a target is the standard voltage (3.6Vx5) =18V, a target is the highest voltage 4.2x5=21V.
2. The 18V battery pack is connected by 5 lithium batteries in series (3.6Vx5=18V), while the 21V battery pack is connected by 6 lithium batteries in series (3.5Vx6=21V), in this case, the voltage of the motor is increased by 20%, and the speed will be 20% faster, only the drill is not blocked for a long time, which will not affect the normal use of the drill. The charging cut-off voltage is 4.2V. 18V battery pack 21V battery pack.
Marked 21v lithium battery, measured 18v, the battery has no problem, but the power shortage needs to be charged.