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Understanding the Nikon D4 battery's lower capacity rating  
Thursday, January 12, 2012 | by Rob Galbraith
Electrifying: A set of EN-EL18 batteries on Battery Charger MH-26. Click to enlarge (Photo by Rob Galbraith/Little Guy Media)
Nikon's adoption of a lower capacity battery for the D4 was a bit of a head-scratcher, especially in a camera that's overflowing with specification improvements. We sat down this week with Toshiaki Akagi, an engineer and senior manager at Nikon in Japan, as well as a key figure in the development of the company's newest pro digital SLR, and got the skinny on why, in the case of the EN-EL18, less is more.

The following information came from an hour-long chat with Toshiaki Akagi that took place at the 2012 International CES trade show in Las Vegas. Akagi, whose title is General Manager, 1st Designing Department, Development Headquarters, Imaging Company, answered our many questions about image quality, autofocus, the XQD slot and more. We'll get the full interview published in the next short while, and it will have some tantalizing bits of information for prospective buyers of the D4. For now, we'll tackle just the matter of the 10.8V/2000mAh EN-EL18's seemingly inferior specs when put against the D3S' 11.1V/2500mAh EN-EL4a.

Akagi cites two reasons for the EN-EL18's emergence. The first is straightforward: a new battery, and new charger for it, was required to be compliant with new battery regulations in Japan. The second is that Nikon sought to build a battery that would not only meet their home country's revised regulatory requirements, but would also surpass the performance of the EN-EL4a.

Less is more

The particular Lithium battery chemistry they ultimately selected for the EN-EL18 delivers greater actual shooting time than the EN-EL4a, says Akagi, despite its lower milliamp-hour rating, when the camera is autofocusing and firing constantly. For example, when a photographer is covering a soccer match with a 400mm f/2.8, or any other situation where the camera is spending more time fully active than idle. When the battery is being continuously pushed to provide current to drive the lens motor, shutter, mirror, image sensor, processing circuitry, memory card and more, Akagi indicates the EN-EL18 will power the D4 through more frames than the EN-EL4a could have, and more frames than the D3S and EN-EL4a too.

Akagi accompanied his explanation with hand-drawn approximations of the discharge curves of the EN-EL18 vs the EN-EL4a at low, medium and high current draws, which showed the EN-EL18 outstripping the EN-EL4a when current demands were highest. The high-current discharge characteristics of the two batteries, he says, are different enough that it enables the 10.8V/2000mAh EN-EL18 to outlast the 11.1V/2500mAh EN-EL4a when the D4 is doing lots of autofocusing and capturing lots of pictures. In this scenario, says Akagi, the EN-EL18 will provide roughly 10% more runtime than the EN-EL4a, at normal temperatures. In cold environments, the EN-EL18's runtime advantage is described as being even greater.

Put simply, if you're using the D4 to take a steady stream of photos, Nikon's contention is the EN-EL18 will give you more frames per charge than would have been possible with the EN-EL4a. Conversely, if the camera is kept awake but is spending far more time idle than it is taking pictures, the EN-EL4a would last longer on a single charge than the EN-EL18.

That said, what sounds like a potential EN-EL4a strength is probably nullified by the fact that the Auto Power Off feature of Nikon cameras will usually be set to kick in after a short period of inactivity. In this ultra-low power state, either the EN-EL18 or EN-EL4a is going to last an extremely long time. So, the fact that the EN-EL4a might last the longest gives it little practical advantage over the newer battery.

The previous paragraphs bring some context to the 2600 frames-per-charge specification for the D4 and EN-EL18, which is a precipitous drop from the 4200 frames a D3S and EN-EL4a are specified to give. These figures are generated using a standardized test developed by Japan's CIPA industry group, and is comprised of shooting one frame at a time with a lengthy pause in between each frame. This synthetic test probably reflects typical consumer-level camera usage patterns well enough, but at the expense of properly simulating how a fast frame rate pro digital SLR tends to be used. It has the effect of emphasizing the low-current charge life of the battery, and results in a much superior number for the EN-EL4a.

But, if Akagi's description of the characteristics of the EN-EL18 are correct - and based on our understanding of how batteries work, his is an entirely reasonable and logical explanation - the real-world charge life of the EN-EL18 in the D4 should end up about matching or slightly exceeding the D3S and EN-EL4a (or the D4 and EN-EL4a, if that pairing were possible).

Eliminating interoperability

This does not, however, explain why Nikon chose to prevent the D4's EN-EL18 and Battery Charger MH-26 from being interoperable with the D3S' EN-EL4a and Quick Charger MH-22. By placing the new battery's and new charger's connector in a different spot, any measure of backwards or forwards compatibility was eliminated.

The reason for this, says Akagi, is the MH-22 (and presumably the MH-21 also) would not be able to properly charge the cells in the EN-EL18 and could cause the battery harm (we didn't get into the specific damage that could occur, or why, though a too-fast charging rate is the most likely thing that Nikon was trying to avoid). To prevent this from happening, the company opted to make a clean break beginning with the D4 and its battery and charger.

Look for more D4 nuggets from our interview with Toshiaki Akagi in the days ahead.
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Related coverage of this topic includes:
  • Firmware update for Nikon 1 J1, V1 corrects slow motion video bug (May 8, 2012)
  • Comparing detail and moire in the Nikon D800 and D800E (April 30, 2012)
  • Nikon issues recall of some EN-EL15 batteries (updated) (April 24, 2012)
  • Nikon Capture NX2 updated to v2.3.2 (April 24, 2012)
  • Nikon D3200 support added to NEF Codec for Windows (April 24, 2012)
  • Nikon to release AF-S 28mm f/1.8G in May (April 19, 2012)
  • Nikon announces D3200, WU-1a wireless accessory (April 19, 2012)
  • Nikon D7000 disassembled (Update: Canon EOS 5D Mk III, too) (April 11, 2012)
  • Nikon posts user guide for Wireless Transmitter WT-5 (March 31, 2012)
  • Nikon Wireless Transmitter Utility updated to v1.3.1 (March 22, 2012)
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