I work nights and go through lots of AAA batteries that power my LED headlamps. But the AAA batteries still have plenty of power left in them,as much as 1.3 volts
So from Green Batteries http://www.greenbatteries.com/battery-adapter.html
I had purchased 4 sets of their battery Adapter/Size Converter Kits that convert AA & AAA to C & D size.
Mainly to convert some AAA's to AA's.
So I have several sets of the C and D adapters that are not being used.
I had purchased some cheap LED flashlights at a "dollar Store" for the triple LED lights for another project.
So I had these AAA battery holders that weren't being used.
2 batteries are inserted in the same direction and 1 battery is inserted in the opposite direction.
I realized that those battery holders would fit in the D size adapters with a little modification.
So I soldered the terminals on both ends of the battery holder to make contact with all 3 post in the same polarity .
Then soldered and filed down a small tip on the "+" end of the holder to make contact with the "+" in the D adapter.
Then inserted the 3 AAA batteries into the holder in the same polarity/direction.
Then placed the AAA holders in the D adapters.
So now I can power a few "D" size gadgets with my excess of AAA's.