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Building an external battery kit for the D1  
Friday, January 5, 2001 | by
Photojournalists covering sporting events shoot a lot of pictures. But their daily frame count pales in comparison to that of the typical event photographer. Peter Wolf, owner of a 5-person outfit called PhotoCrazy, typically shoots thousands of photos in one go. At a one-day event later this month, for example, he estimates that 6000 frames will click by on his Nikon D1.

As a result, Wolf chose to develop an external battery arrangement for the D1 that would eliminate the need to change D1 battery packs 10 or more times during a single shoot, as well as eliminate the hassle of storing and charging that many batteries at an event. In the first round of testing, Wolf squeezed off about 2000 JPEG Normal frames in succession without a significant drop in battery voltage. While he hasn't yet tested the external battery under field conditions, he's optimistic that for his purposes he'll be able to shoot 3000-4000 photos before swapping in a new battery pack.

Peter Wolf's D1 and external battery pack. Photo by Peter Wolf/PhotoCrazy.

Wolf initially had thoughts of turning his external battery solution into a retail offering, but decided this morning that such a product would stretch his company's resources too thin. Instead, he's chosen to release detailed instructions so that other D1 users may build the battery kit themselves. If the kind of D1 photography you do would benefit from lots of battery juice on hand, and you're not afraid of a soldering gun, read on.

Obligatory disclaimer: Nikon tech support pointed out the obvious to Wolf when he first broached the idea of an external battery pack for the D1: in the event the camera is damaged through the use of this battery, which would likely be the case if the connector cable weren't assembled properly, you're on your own. Neither Nikon, Peter Wolf nor I will accept responsibility for the damage. You'll be 100% liable for the cost of the repair, even if your D1 is still under warranty. If that isn't acceptable to you, please don't attempt to perform the modifications described in this article.

Purchasing the battery

The 2.8 pound, 4.9" x 2.6" x 2" lead acid pack that forms the core of the kit is from Bescor's MXC series of batteries for Canon and JVC digital camcorders. Model MX-5C is the one that Wolf selected. Its power rating is 8 Volts, 34 WattHours (4 AHours) and 4.2Amps. In other words, this is a seriously powerful battery. Its soft case includes a belt clip and zippered top.

Bescor MX-5C soft case.
Photo by Peter Wolf/PhotoCrazy.

The battery may be purchased with an overnight, 110-volt AC charger (Bescor model ATM-JB) that automatically shuts off when the battery is fully-charged. The battery and ATM-JB charger together is Bescor package MX-5CATM, and is the combo that Wolf has used thus far. It's possible to purchase the MX-5C battery without a charger (Bescor model MX-5CNC), then select from one of four different ones Bescor produces for this battery, including a quick charger and a charger for European (220v) use. See Bescor's web site for more information on the chargers available and battery charging times.

Bescor indicates that there are three dealers that ship their batteries across the US, and perhaps to Canada and overseas as well:

  • B & H Photo Video in New York, NY. The 800 pound gorilla of mail order photo retailing stocks Bescor's full line of batteries, though most are incorrectly listed on their web site as being sold without a charger only. A Bescor representative recommends that you call B & H directly to order the MX-5CNC battery and select from one of the available chargers. B & H sells the battery and ATM-JB charger (that's Bescor package MX-5CATM) for about US$130; the battery on its own is about US$95. B & H may be reached at +1 800-606-6969 or +1 212-444-6615.

  • Elite Video in Hot Springs, Arkansas. Elite Video may be reached at +1 800-468-1996.

  • Voice and Video in San Diego, CA. Voice and Video's sales line is +1 858-467-7111.

To find out if a dealer in your area carries Bescor products, send an email to

Making the connection

Wolf's battery plug's into the D1 via the same port as Nikon's EH-4 AC adapter (below).

The D1's DC input jack, with connector
inserted. Photo by Peter Wolf/PhotoCrazy.

This plug is proprietary and, as Wolf has discovered, not easy to find. As a result, Wolf has fashioned a new cable, built from the EH-4's connector cable, that enables him to connect one end to the camera and the other end to either the Bescor battery or to the EH-4. As you've probably surmised, assembling this pack means purchasing the EH-4 AC adapter in addition to the battery.

You'll also need two connectors:

  • A DC coaxial plug. This connector attaches to the end of the cable that's been snipped from the EH-4's connector cable. Once attached, this cable can then plug into the socket on the Bescor battery. Wolf used a Philmore DC Coaxial Plug, 2.1mm (ID) x 5.5mm OD, no 210, though any good-quality brand of DC coaxial plug should be fine.

  • A DC coaxial jack. This connector attaches to the severed end of the cable that should be left attached to the EH-4 AC adapter once surgery has commenced. Wolf used a Philmore DC Coaxial Jack, 2.1mm pin x 5.5mm (ID), no 257, though any good-quality brand of DC coaxial jack should be fine.

Once the connectors are attached, the EH-4 AC Adapter and modified cable should look like this:

Modified cable with DC Coaxial Plug attached (lower left), ready to be plugged into
the socket on the Bescor battery, or into a DC Coaxial Jack fitted to the severed
end of the EH-4 adapter's connector cable (right). Also shown are the Philmore
plug and jack that Wolf used, though any good-quality jack and plug should work.
Photo by Peter Wolf/PhotoCrazy.

Once you've cut the EH-4 AC Adapter's connector cable, ensuring that you've left several inches of cable still extending out from the EH-4, Wolf offers these tips on making the modification:

The cut cable has two wires in it. (NOTE: The plug going into the D1 actually has three connections but one of them, the middle one, is not used) There is a red wire and a black wire. Solder the red wire to the center tap of the DC Coaxial Plug and the black wire to the other lead of the Coaxial Plug (below).

DC Coaxial Plug wired to the end of the cut EH-4 connector cable.
Photo by Peter Wolf/PhotoCrazy.

I recommend wrapping a piece of insulator around at least one of the soldered terminals (as shown above) to avoid shorting the battery in case the cord gets twisted or pulled on. Care should be taken to get the plug cover over the cable insulation after assembly for added strain relief. The final assembly picture shows the cable insulation about 1/16 inch from the plug cover. If we were to do this again, we would try to avoid that 1/16 gap. Getting a longer plug cover may solve this problem.

WARNING: Don't mess up on the polarity when soldering the connector - you'll be sorry. Double check that the red wire goes to the center tap and carries the positive voltage!!! Double check and triple check with a Voltmeter that you're getting the proper polarity at the plug that goes into the camera!!! The reason for cutting and splicing the charger cable is that the plug from the EH-4 AC Adapter that goes into the D1 DC Input seems to be a custom plug for Nikon. I have inquired with all the major connector manufacturers (about 10 so far) and none have that type of plug in stock.

Soldering a mating DC Coaxial Jack to the cut cable on the EH-4 AC Adapter is a recommended option which will allow one to salvage the AC adapter if need be. The EH-4 AC Adapter is obviously NOT needed with the external battery and should never be used in an external environment per Nikon's instructions. These are probably safety precautions since the Adapter produces a lot of current.

OK, that's it! Simply plug the DC Coaxial Plug into the new external battery and plug the other end into the D1 at the DC Input.

Bescor battery with modified connector cable inserted.
Photo by Peter Wolf/PhotoCrazy.

Turn the camera on and shoot away without worrying about battery power. It is recommended by Nikon to turn the camera off before disconnecting the DC input connector from the camera. I recommend leaving the NiMH battery in place while using the external battery. I did notice a slow drain on the NiMH battery with the external battery in place. From our experience with using external batteries on our Olympus 2020's, we normally replaced both the internal and external batteries once the camera indicated low voltage. However, that happened so seldom that not much data or logic is available for those situations.

One final word of caution is to treat this external battery with respect. There is a lot of power stored in a small volume. Avoid any possibility of shorting out the battery by keeping all small conductive objects away from the battery connectors. Handle the cables carefully to avoid strain and possible shorting at the solder points. The battery does have a circuit breaker build in. Keep the battery away from children and don't use it as a hammer since acid may spill out of it.

If you're squeamish about assembling the connector cable, Wolf indicates that's he prepared to offer assistance. Contact him at If you know of a source for the EH-4's proprietary connector, he'd welcome information on that too.

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