This is normal. The way the system is designed, the supply voltage will
equalize itself to the right amount under the proper load. Your meter
alone is not properly loading the supply.

As for your old drill, the batteries probably went defective, and thus
also damaged the power pack. Don't try the power pack from the new
drill to the old one. It is possible to do some damage, or encoure a
safety issue.

Jerry G.
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