I’d never heard of D shells before. The idea is, you put one or two AA batteries in one of these D battery-sized shells, and use the AA-filled D shell in place of a regular D battery.
My question is, will stuff work properly with this substitution?
It looks like I’m going to have an ongoing need for D batteries, so I was looking to see if Eneloop, my favorite brand, had rechargeable D’s. They do, but they’re expensive. (Like $25 each on Amazon. Ouch.) But my search on Amazon turned up lots of these shells, which are really cheap. It would be a hell of a lot cheaper to use Eneloops or other AA rechargeables, which I’ve got a good supply of already, in these shells, rather than buying D rechargeables. And I really don’t want to buy non-rechargeables anymore if I can avoid it at a reasonable cost.
So if I’m powering, say, a wireless stereo speaker with AA-filled D shells, any reason why it wouldn’t work as well as if I was using D batteries?
Back in the mid-80’s I had some GE rechageable batteries that worked on that principal. The AA size was charged and put into a “D” adapter.
I had a boombox that went through D batteries like crazy, so I tried the GE rechargeables. At the time I thought it worked quite well and saved me a boatload of money on batteries.
You could probably get away with using normal NIMH D cells if you’re going to be using a lot of batteries, since there may not be time for substantial self-discharge to occur. Also, I don’t know what products you’re using, but most consumer electronics are meant for use with alkaline cells. NIMH batteries have lower capacity than alkaline, Eneloops lower still, and eneloops in a shell even lower. I’d run the numbers on that to see how much capacity you would actually get.
I did the same thing with AA-filled C shells and it worked fine. I ended up rarely using the speakers on battery, so I was glad that I did not spend the money on bigger rechargeables. If you know that you are always going to be running on batteries, it may be worth the large capacity of the real D cells.
Well designed stuff works great that way. Some devices have issues with the initially lower voltage but that means they already waste a lot of power in the alkaline cell. (Alkaline spends a good chunk of it’s discharge below the voltage of the NiMh even though it starts higher.) Some particularly crappy devices depend on the natural current limiting of the alkaline cells due to higher internal resistance. If that’s the case you can have issues because the Eneloop will push too much power.
Devices with power meters are pretty much wrong for NiMh. Voltage is not a good proxy for remaining capacity on NiMh and the meters are usually set up for the voltage curve of an alkaline.
IIRC you can also find shells that take 3xAA but they tend to be a touch big for some devices. It might be worth hunting around to get the extra capacity.
yes, it should work fine. the voltage a battery produces is defined by the cell chemistry. An alkaline battery will produce 1.5 volts no matter how large the cell is. NiCd and NiMH cells produce 1.2 volts no matter the size. What making a larger cell gets you is higher current capacity (some call it “ampacity,” I don’t because it sounds dumb.) This is what is measured in mAh (milli-Amp*hours.) A NiMH AA battery usually has about 2000 mAh of capacity. A NiMH C-battery has about 5-6000 mAh, and a NiMH D-cell has about 10-12000 mAh.
so yeah, running a device which expects D-cells on AAs with shells will work fine, but it’ll only run as long as an AA will allow it.
ETA: if you’re in a store and you see NiMH “D” cells on the shelf which only have about 2000-2500 mAh capacity, they’re just AA cels in a non-removable D shell. total waste of money.
Found one that’s probably not worth it at 9.95 apiece before shipping. If you look make sure what you find is parallel since my quick search also showed up series 3xAA to D adapters (with 3 times the voltage of the D Cell).
Surely you wouldn’t put more than 1x AA batteries in one of these D shells? Man, that’d like have your voltage all off and stuff. Wouldn’t it?
Or, if the unit is expecting 1x D battery and you try to power it with 2x AA batts, it’d be getting ~3 instead of the 1.5volts that it was expecting. What am i missing?
It only would impact your voltage if you put them in series. The shells put them in parallel.
Batteries in series adds the voltage of the batteries.
Batteries in parallel is the same as using a larger battery of the same voltage.
There are multiple ways to go about this- the rechargeable D route, the AA –> D shell that just fits a single AA, and the 3 AA in parallel option.
The standard to measure against is the average alkaline D cell with a capacity of something like 12,000 mAh at a nominal voltage of 1.5v.
Most rechargeable D cells have capacities in the 2500 (Energizer) to 5700 mAh (Eneloop) range. On the low end, that’s essentially the same as an AA battery. This is assuming low self discharge batteries- you can get high capacity non-LSD batteries, but they’ll self-discharge pretty rapidly if you don’t use them.
These are good if you need LSD batteries, but they’re expensive.
The AA –> D single battery shell basically gives you a D battery with the capacity of an AA rechargeable, which is 2000-2500 mAh @ 1.2v They work, but you’ll be replacing your AA battery about 6x as often as alkaline D cells.
The 3 AA in parallel gives you the capacity of 3 AA batteries @ 1.2v, so between 6000 and 7500 mAh @ 1.2v. This is a reasonable capacity (1/2 of the alkaline battery), and lets you sub in other AA batteries if need be.
that’s because they are AA cells, just in a non-removable D-size adapter. The Eneloop ones are probably sub-C cells (the ones R/C car packs are made of) also in a D adapter.
One thing with AAs in parallel is that they are only as strong as their weakest link, in a sense. If one cell starts to go early, it will start to drain juice from the other cell(s). Unless there are diodes in the shell to prevent this.
Given the extra demands put on the cells, this is more likely to happen in this situation.