Bests & Worsts Reviews from Amazon

The D spacers in this product (Panasonic BQ-BS1E4SA Eneloop D Size Spaces) feature large negative terminals like that found on real alkaline D cells. This is a big improvement over the previous version of eneloop AA-to-D Size Spacers/Adapters, which rely on the negative terminal of AA cell as base. See the photo I uploaded for size comparison. When using the old D spacers in my MagLite ST3D016 3-D Cell LED Flashlight, for example, the battery spring is too large to make proper contact with the base of AA cell. But the new D spacers worked perfectly. Using those D spacers also makes my Maglite a lot lighter, which is a good thing - as long as I don't need to use it as an impact weapon. On the other hand, it is important to note that the energy stored in a real alkaline D cell is about 5-8 times greater than that in a eneloop AA cell. A typical alkaline D cell is rated for 18,000mAh when supplying a light load of 50mA. When used in a heavy-load appliance such as Maglite, the battery capacity drops to around 10,000mAh. Still, this is 5x higher than the capacity of a 2000mAh eneloop AA cell. Therefore I can expect just 4 hours of runtime from a set of three rechargeable AA cells, compared to over 20 hours from three alkaline D cells. If longer runtime is important to you, consider D spacers that can accept two AA cells in each shell. Doing so effectively doubles the runtime. I have tested an inexpensive product and found it to work in my Maglite - after some modifications. See my review on AA to D Size Battery Adapter Case for details. [Additional Notes] - On the back of the new eneloop spacer it says "Insert only a Panasonic rechargeable battery" and "Never insert a non-rechargeable battery" (in Red). The fact is, you can insert any brand of rechargeable AA cell into this spacer. You can even use non-rechargeable alkaline AA cell in case of emergency. I do not see any potential danger in doing so, although the battery life will be very poor. - The same product (BQ-BS1E) can be found in the box set Panasonic Eneloop Rechargeable Batteries & Charger (917976)