Battery Adapter - an excellent invention

I often need 1.5 volt D-cell, this big thick batteries, for a lamp. These batteries do not exist everywhere to buy
and are expensive. This adapter can be a single cell by, or rather replace two AA batteries. The Voltage
remains the same at two parallel-connected batteries, only the capacity has doubled. Thus one can assume that
the batteries should last twice as long.
Furthermore, the adapter will register, they sit properly and must be handled with practical clip fastener. In addition, very
inexpensive!