DIY AA Eneloop to D cell adapter

thread on another forum got me thinking....my tent fan "motor" for my ceiling fan will run 9 hours on a new D cell, but only slightly more than 3 hours on a AA Eneloop in a single cell "D" adapter... I ordered a set of the dual cell adapters, but haven't received them yet...so I put together a proof of concept, using a couple of sheet metal screws and fender washers to produce a "pack" to increase the milli Amp hours available... the pack does not need to fit in a cylindrical tube, so went with a 4 pack...the sheet metal screws are to keep the washers centered...the section of plastic tubing is a spacer... pack is held together with a piece of bicycle inner tube





I ran a duration test, and the pack ran the fan motor for 9 hours, my desired outcome, but upon recharging the Eneloops, found one had not been discharged, so evidently had not made electrical contact... so the old "three points determine a plane" has some merit... I have a much smaller bicycle inner tube, and will try a 3 pack tomorrow...which should fit in a cylindrical flashlight body...the space between the 3 batteries is quite small, might possibly find a couple of roofing nails with large enough head, or try some pre 1982 copper pennies for contacts...regards

Thomas Edison, Henry Ford, Les Snyder. great minds!

Mark I Mod I.... I'm done... cut a section of small bicycle inner tube 2 3/4"... insert 3 Eneloop AAs.... center in tubing, there should be about 3/8" over at each end... insert a quarter (heads out for + and tails for -)at each end to act as terminals...they are held in place by the excess bike tube.... to insure better contact at the (-) end, fold a piece of aluminum foil several times... insert between the flat ends of the cells and the quarter as they don't make as good of a connection as the positive end... you may need to add a couple of pennies (pre 1982 are copper) to the positive end to make a connection...or trim to fit... will fit in a D sized flashlight tube

My compliments, sir. I am fresh from an unsuccessful attempt to replace the rechargeables in a waterpik, and admire your field expedient prowess.

Neat solution. My thoughts go towards the mixing of metals for the contact surfaces. I am not sure if it creates a high resistance/heat generation situation. Anyone with knowledge (physics or chemistry) to either confirm or dismiss my fears please chime in.

At low voltages/currents like this, there may be additional resistive inefficiencies but I doubt a big heat buildup would occur. However, I would be strongly inclined to remove any corrosion-resistant coatings on a contact (such as the galvanizing on a roofing nail).