[TheForge] Two electrical questions

[Barking Crow]

Several months ago I found a complete craftsman professional 18volt 
drill/driver in a trashpile in its case but with a frozen chuck that despite 
lots of work I could never fix and finally failed cutting it apart to get to 
where I could replace it.  Then yesterday in a trashpile I found a craftsman 
14.4 volt drill/driver, battery, charger, and neat flashlight.  The battery 
is so weak that it will just barely make the filament glow.  The 18volt 
batteries are strong and will spin the chopped up chuck strongly and hold 
their charges well.  So today with some creative belt sander and chisel work 
I got the 18volt batteres to fit onto the 14.4 volt flashlight which has a 
very nice adjustable head and the light is bright.  Is there a problem using 
the more powerful battery?  What should the filament care about 3.6 volts? 
AND, should I try similarly modifying the drill base to fit the 18 volt 
battery?  How will the motor feel about the extra 3.6?  Nothing ventured 
financially.  I feel certain the craftsman boys will tell me not to do it, 
but what do you guys think?  Thanks,

Jeff in already hot Tallahassee