This Sanyo Eneloop AA Rechargeable Battery "D" Spacer Kit includes 2 AA batteries and 2 "D" battery spacers. Just plug the Eneloop AA battery into the spacer and you can use it in equipment that requires a "D" cell battery. Of course, the spacers only adapt the mechanical dimensions of the Eneloop (length and diameter) and not its electrical characteristics. The voltage and the capacity remain unchanged from the Eneloop AA specification.
Sanyo Eneloop AA Rechargeable NiMH Batteries combine the advantages of disposable batteries along with the advantages of rechargeable batteries. Because the batteries have a low-self discharge, the batteries are shipped charged and ready to use. The low self-discharge design allows you to store the Eneloop batteries for months and they will still provide almost full capacity and performance. Even after being stored for 1 year, the battery holds 85% of its charge. When charging the batteries there isn't any memory effect, so you get a full charge every time. The batteries have a life cycle of around a 1000 charges.
One of the main features of Eneloop batteries is that they operate at higher voltage levels. Many applications switch off or show the low battery signal if the voltage is lower than 1.1V. A traditional NiMH battery will lose its voltage at this critical level. Eneloop batteries, however, will keep the voltage level over 1.1V for a long time. That is why Eneloop batteries last longer than a standard 2700 mAh battery.