Instruction: Extract information from the supporting document to answer the given question.

Input:
Question: Do these adapters hold one AA battery per shell or two for higher capacity?
Document: So it's $6.99 for a single plastic shell? Seriously?How many adapters come in a package? One, as the product description seems to indicate? Or four, as there are four adapters displayed in the picture? Or two as one reviewer stated he received?Also, I seriously doubt that the weight of this package is "8 pounds" as mentioned in the product description. Are these adapters, like, from the future?
The AA batteries don't last nearly as long as the D cells, but for my purposes, that's okay. So far, my two main uses of these adapters have been to allow my kids to use the flashlights for play without wasting alkaline D batteries, and to provide a handy emergency backup if we need a flashlight and don't have enough D cells available. I have a ton of rechargeable AAs, so these affordable adapters should mean I'm never without a flashlight battery when I need one.
None of the other depths are important, just to hold things in place). On your 12" rod, drill a 1/4" hole on one end about 1/8" deep (do this for D-cells only, not needed for C-cells).That's it for the jig. Now you're ready to make dozens of adapters in no time.FOR C-CELLS:  Cut 1" PVC into 1.8" lengths (shorter than AA bty).
So the larger spring in a battery compartment may not make good contact with the AA cell bottom. Usually this problem can be solved by inserting a copper penny between the spring and the battery.There are rechargeable NiMH D-cells available with capacity up to 12,000mAh. Those cells can out-last alkaline D-cells in large current applications. However, those cells are expensive (around $25 for two) and you need special charger that are designed to charge high capacity D-cells.
You receive four (4) AA to D battery converters as picturedYou get what you pay for in this case. If you are looking to convert your standard 1.5 volt AA batteries this is an excellent option. If you are unaware, AA batteries are cheaper but D size batteries contain and maintain a longer charger.The product itself isn't very complex. It is essentially a plastic shell with no back. The shell will hold the AA so that it is level with the battery holder/ + and - ends.
This may not be a problem in many cases, but if you're using, say, a Mag-Lite that accepts D batteries then the spring that is the negative contact on the flashlight is too wide to hit the smaller negative end of a AA battery. So you'll need to put something in there to make the contact. A penny is what I used.Other than these two issues, these adapters work well.
I was pleased by the light weight and the ease in which the AA batteries fit inside and clicked into place. I have a battery operated fan to use to distribute heat from my gas fireplace insert in case the power goes out and I didn't want to keep a bunch of heavy D size batteries around.I used the Lenmar adapters with AA batteries and got 8 hours of performance from one set which to me is great.I fully recommend this product to anyone.
For uses that do not need the capacity of a D cell such as LED lights this product is the answer. I read reviews of other brands and chose this one for its simplicity and longevity. I bought these along with an LED lantern that requires 4 D cells. I too had the problem where the AA negative end was not big enough but I found the solution. My C***man lantern has 4 batteries in a pack instead of stacked end to end like a flashlight.
This is because the capacity of a typical NiMH AA cell is only about 2500mAh. In comparison, a typical alkaline D-cell is rated at about 20,000mAh for low current applications. At higher current, the actual capacity may drop to half. But this is still four times as much as that of a NiMH AA cell.
I got these because they are cheaper than the eneloop adapters of the same type. What I found is that these hold the battery more snugly and prefer to use them for that reason. Don't pay more. These are the best price and the best value.
Answer: They hold only one AA battery per shell.