A 12v pack of nicads is actualy discharged at 12v, 13.2 v 13.5 or so
would be 100% charge. A 12v input would never charge the pack. Using a
higher V is ok the real issue with any pack is not over charging it. Its
a Master Mechancrap, who ever that is, it likely does not have a peak
detection charger , standard with quality equipment that stops charging
when battery voltage begins to drop and chemical conversion of electrons
goes to heating and ruining a pack. 2 ways to test a fully charged nicad
pack is 1 when pack warms, but being in a charger producing its own heat
this is impossible, pack must be charged by wire leads. 2 is voltage
drop. packs increase in voltage till 100% charge is met, then actualy go
down in V as heat is now the conversion of electrons. Go by time or hook
up a V meter and monitor. I still have Makita packs from 93 that work
but have ruined 1 yr old packs on non peak chargers Tool manufactrers
dont tell you this as they make their big money on selling you a new
pack. Time is another fairly accurate way to keep from ruining a pack,
usualy 1 hr , but all chargers are different, never leave it in a non
peak charger, it just cooks the cells slowly.