A D battery (D cell or IEC R20) is a standardized size of a dry cell. A D cell is cylindrical with an electrical contact at each end; the positive end has a nub or bump. D cells are typically used in high current drain applications, such as in large flashlights, radio receivers, and transmitters, and other devices that require an extended running time. A D cell may be either rechargeable or non-rechargeable. Its terminal voltage and capacity depend upon its cell chemistry.
The National Carbon Company introduced the first D cell in 1898. Before smaller cells became more common, D cells were widely known as flashlight batteries. The U.S. military designation for this battery has been BA-30 since sometime before World War II.[1] During World War II, it was designated the Type C battery by the U.S. Navy, leading to confusion with the smaller C cell battery (BA-42).
In 2007, D batteries accounted for 8% of alkaline primary battery sales (numerically) in the US. In 2008, Swiss purchases of D batteries amounted to 3.4% of primary and 1.4% of secondary (rechargeable) sales.[2][3]
D, C, AA, AAA, AAAA and 9-Volt batteries
Dimensions and capacity[edit]
Battery capacity and size[edit]
A battery's capacity depends upon its cell chemistry and current draw. Duracell brand rates its alkaline D cell performance as approximately 20,000 mAh at 25 mA draw, but about 10,000 mAh at 500 mA draw.[4] This effect is generally less pronounced in cells with NiMH chemistry and hardly at all with NiCd. Many commonly available size D rechargeable cells are actually sub-C cells in a D-sized holder.
D batteries have nominal diameter of 33.2 ± 1 millimeters (1.3 inches). The overall length is 61.5 millimeters (2.42 inches).[5]
As battery technology continues to expand, you may be confused by the many options out there as you peruse the end cap where you buy your batteries.
Because larger batteries are more costly, you want to buy the right size and the right chemistry.
Differences Between C & D Batteries
Size is the main difference between C & D batteries. C batteries are shorter by 11 millimeters and slightly smaller in diameter. The big difference in size to consider is output.
While C batteries are designed to be used in toys and small flashlights, D batteries can power large flashlights, alarms, and radios for longer periods.
In the event of an emergency, it is possible to stretch the length of a C battery so it will fit into a D gap with a quarter at each end.
However, as D batteries can produce more than 17,000 mAh or milliamp hours and C batteries produce only 8,000 mAh, the fix may not work for long.
Don’t try to rely on this extension for long; replace the C batteries and the extension as soon as possible with batteries of the right size and output.
Additional Options to Consider
As of November 2022, you can expect to pay a little over $1.00 per battery for disposable D cells in bulk. A single rechargeable D cell batter will run about $6.00 in a pack of 4.
However, rechargeable technology is getting both more effective and cheaper to buy. If you can justify the expense for a tool that sees regular use, investing in rechargeable batteries may be a smart choice over time.
A single disposable C-cell battery, purchased in bulk, will run about $.75 cents. The same size and output in a rechargeable will cost about $4.00.
The key to justifying the switch may be the conditions in which the tool or toy needs to function.
Safety Note: Never try to recharge a non-rechargeable battery. The chemistry will fail and you could be injured should the battery casing rupture.
How to Protect Your Batteries
Cold, moisture, and corrosion are all very hard on batteries. If you live in cold areas and you store your flashlight in the car, consider pulling the batteries and storing both light and batteries in a breathable tote.
Batteries left inside tools can corrode and leak, damaging both the other batteries and the electronic components of the tool.
It’s also a good idea to get on a schedule of testing your batteries and swapping them out as they fail.
If you have a good quality flashlight in all of your vehicles, getting in the rhythm of checking the tool each spring and fall can help you stay safe should a vehicle fail or a tire blow during your commute.
If you have an alarm that is powered by a D battery, consider testing more often. Because the draw on a D-cell battery is so large, you may find that your alarm fails for lack of power in a very short time. Consider testing monthly, swapping out more frequently, and disposing of batteries safely.
Environmental Considerations
It’s important to note that disposable batteries are not a sustainable product. They take more power to produce than they actually provide.
At the end of the lifecycle, an unrecycled battery can release toxins into the environment that will contaminate the soil for years to come.
Unless the application absolutely requires a large, heavy-duty tool that can only be powered by disposable batteries, it may make more sense to invest in rechargeable units.
A small rechargeable flashlight, mounted near an outlet, can actually be easier to find than the one you keep in the junk drawer.
Of course, such tools do run the risk of becoming electrical vampires. If a charger or a rechargeable item is plugged in within your home, it’s drawing some power.
If keeping your electrical footprint as low as possible is important to you and your family, a small solar panel dedicated to your rechargeable flashlight may be the simplest and least costly option.
If you’re on the fence about disposable vs. rechargeable C & D batteries, consider this: You can get about 36 hours of steady use out of D batteries.
The same rechargeable battery should last for 3 years. Disposable batteries, unused, have a similar lifespan before their power is expended through lack of use.
If you need to use the tool regularly and will burn through those 36 hours repeatedly in three years, you may come close to recouping the cost of the rechargeable batteries within the first year.
Getting the Most Out of Your Investment
Battery technology has changed a great deal as the market for rechargeable technology has expanded. There may still be tools and toys that you have to power with a disposable battery.
As soon as you buy a pack of batteries, date it. After 3 years, even unused batteries can fail. Instead of investing in large packs of batteries that may or may not get used up in time, buy only what you need for a single application.
Shop for rechargeable technology when and where possible to avoid investing in batteries that will just need to be recycled in a few years.