I have a bathroom scale which uses a 3v CR2016 battery. The battery only lasted about a month before needing to be changed. I thought that perhaps I was getting old batteries from stores, so I bought from a variety of stores and they all died quickly. My solution was to find the wires going to battery, and splice in a 2 AA battery holder from some old device I had. So I replaced the 3v CR2016 with 2 1.5v AAs in series. This worked quite well. My question is if this is safe to do in other places. I didn't really care about the scale, but I may do this with some more expensive electronics. Is this fine to do as long as I match the voltages? I plan on replacing anything that can take AAs or AAAs that currently takes watch batteries and doesn't need to. Also I may think about running some devices I want longer battery life out of on Ds instead of AAs. So would all this be fine? I won't be doing anything crazy like trying to start a car from 8 AAA batteries.