D Batteries. Bigger not Better?

[wuyeah]

Seems like newly super bright 1000+ flashlights are with C123 or 18650 batteries. How come D type batteries lost its charm? What is the science behind?
Why isn't RRT-3 triple XML (for example only) not use 2xD batteries instead of 6xC123 or 3x18650 instead. The housing is not exactly small.
Batteries, Bigger is not better in terms of power?

 

[yellow]

because in 3*18650 there is more power inside, while the whole package is smaller than a 2*D light

 

[H-Man]

Too low of voltage, and alkaline batteries can't provide as many amps as nickel and lithium chemistries due to internal resistance.

 

[JohnJack]

Fenix TK50, also TK60 and TK70. Maglite 2D.
Alkaline and zink-carbon D cells are superior in runtime-per-dollar, but only at low current. NiMh D are either an AA cell in a bigger shell or cost too high or both. So 18650 are more common, cheaper and provide much more power than D.
There are Li-Ion 26650 cells that are bigger than 18650 thought slimmer than D. Several flashlights of that size appeared last year so fat cells are gaining some popularity again.

 

[StarHalo]

Bigger is better in terms of runtime, generally speaking; during a week-long power outage, 40 minutes of 1000+ lumens suddenly isn't nearly as impressive as the simple D-cell light that can be left on all night long..

 

[Vortus]

Depends on what your after. Have to move to an M class lion to match a D Nimhs capacity.

 

[Cataract]

I'm surprised no one has mentioned this yet:

Most (if not all) store-bought D batteries only contain around 3000mAh, which is barely more than a rechargeable AA NiMh LSD at 2100 mAh that you can get from the same store. A good rechargeable D battery can contain up to 11 000 mAh, which is a lot more energy than an 18650. I think the availability of good D batteries is a barrier to great D sized flashlights.

 

[DM51]

Moving this thread to the Batteries section, where it should have been posted...

 

[Mr Happy]

I'm surprised no one has mentioned this yet:

Most (if not all) store-bought D batteries only contain around 3000mAh

It has not been mentioned because it is not really correct. The capacity of an alkaline battery depends on the discharge rate, but there is an ultimate capacity achieved as the discharge rate is reduced. For an alkaline AA cell the ultimate capacity is about 3000 mAh. For an alkaline D cell it is multiples higher, somewhere around 15,000 mAh. Of course you won't actually get 15,000 mAh out of a D cell unless you discharge it at a very low rate like C/50.

(Unless, perhaps, you are referring to store-bought D size NiMH batteries, which I guess might be the case on thinking about it some more. But most people think of a D cell as an alkaline cell.)

 

[broadgage]

A premium brand alkaline D cell contains up to 18 A/H on slow discharge.
D cells are therefore often the best choice for long run time lights of modest power use.
For example I have a light that uses 6 D cells and a multi voltage 1 watt LED lamp. The light output is greater than a standard incan, and the run time about 100 hours. Clearly a good choice for long term blackouts, 100 hours of simple and reliable light from £10 worth of readily available batteries.
Alkaline D cells can supply several amps, but only for a very short run time. For currents of more than about 1 amp, lithium or rechargeable cells will normally be a better choice.
Even at 1 amp, less than half of the theoretical capacity will be available.
At 0.15 of an amp, virtually all the 18 A/H capacity is available.

 

[fivemega]

Bigger is not better in terms of power?

As long as they both are same chemistry, bigger battery could be better than smaller one.

A good rechargeable D battery can contain up to 11 000 mAh, which is a lot more energy than an 18650.

Not really.
NiMH D cell .......... 1.2V @ 11000mAh = 13.2 Wh
Protected 18650 ... 3.7V @ 3100mAh = 11.47 Wh

 

[Mr Happy]

NiMH D cell .......... 1.2V @ 11000mAh = 13.2 Wh
Protected 18650 ... 3.7V @ 3100mAh = 11.47 Wh

While true, a typical light of reasonable form factor might contain 2 D cells compared to a single 18650, so then you would get twice the run time, albeit in a much bigger light.

 

[fivemega]

While true, a typical light of reasonable form factor might contain 2 D cells compared to a single 18650, so then you would get twice the run time, albeit in a much bigger light.

In most cases such as 2D M*g, you can accomodate 2 protected 18650 cells in 2D
Pair of NiMH D cell .......... 2.4V @ 11000mAh = 26.4 Wh
Pair of protected 18650 ... 7.4V @ 3100mAh = 22.94 Wh

Let's say a truly regulated flashlight works well at highest brightness from 2.4 volt to 7.4 volt.
Do you admit that tail current with 2D will be (about) 3 times of 2x18650 ?
If current load on each 18650 is (say) 3 amps, then load on each D cell is about 9 Amps
Switch, tail spring and all electrical connectors of D cell flashlight must be capable of 9 Amps while for 18650 cell they should be capable of only 3 Amps
Voltage loss in high current flashlights are more when current draw is high.
2x18650 version is much smaller in diameter and light weight.
If discussion is about 2D barrel, then 2x26650 or 2x32600 wll be way higher energy.