I occasionally stop by Harbor Freight on my way home from work. I like to use their rechargeable batteries for testing just in case something goes wrong. Then if something does go wrong, at least it is not one of my eneloops. Well today I decided to buy two packs of their D batteries, which come two in a pack, for a total of 4 batteries. When I got home my curiosity got the best of me and I decided to open one of them. I had seen/read about the Energizer D and knew eneloop uses AAA's and AA's in their C's and D's (as seen in the pictures below).
So I was not surprised to find an inside similar to the energizer D.
I was surprised however to see it held in place by rosin (not even a plastic holder like in the energizer). I decided I didn't actually need the D size so why not open another one and have a pair of the smaller inside batteries. Another Surprise!!
This next one did not match the first. It had 4 AAA's in parallel (noticed in the second image above how close the metal tab is to shorting to the outer casing! It is less than a mm. Not very safe! And considering they are only held in place with rosin, which softens when it heats up). I figured they must have switched the design at some point and I must have ended up with 2 D's (one pack) of this style and 2 D's of the other. I decided to open them all up. Yet another Surprise!!!
3 AA's in parallel. Talk about inconsistency! I only bought 4 batteries and yet 3 of them were not the same. On top of that, they are all supposed to be D's. Another thing is the 2500mAh advertised capacity. It makes sense for the first one I opened (and maybe even for the 4 AAA's because they would show a decreased capacity under the loads normally seen by D batteries) but the 3 AA's would actually have a capacity much greater than the advertised 2500mAh. Use all these in series and one of them is bound to be driven into reversal.