Here is the "dream" solution"

• a high-capacity Li-Ion battery with regulated & protected 9V output capable of delivering 5A and a connector to match the Nikon body (that package would need to include a small AC-adapter to recharge the battery)

Compare that to the most practical, cheapest yet easiest & most reliable solution: /stargazer95050/31956033

• any 12V battery -- preferably _NOT_ Li-Ion because most of these batteries have limited output current and require very special chargers
• An AC-inverter ( < 100W to power a camera and similar battery chargers)
• Camera-specific AC power supply, similar to the EH-5(b)

The downside of it : it is HEAVY & BULKY, has additional components
But it is reliable, has been tested and is not expensive when you assemble it yourself. You can find an off-the-shelf solution when you look in the car-accessory ("jump start battery AC inverter"). Similar, you can find useful gear when searching for "Power Tank" .

There are a couple of solutions in between and my "Canon-fodder" is one of them. Adapting that to Nikon isn't difficult. My solution wasn't cheap, mainly because of the Li-Ion battery but by now, the battery prices now have come down.
When a camera has a DC-input, but you cannot find a matching connector, it may just as well not be there. davidkinghamphotography and many others have circumvented that issue by using dummy batteries and my modification for the Canon is not much different. The price for those dummies varies and it may be even worth it to buy an AC-adapter just to get the "dummy"

Building a near-perfect solution

• PICKING THE POWER SOURCE / battery => NO ASSEMBLY REQUIRED
  There are 7.4V and 9V solutions but in nearly all cases, they don't provide the 4A...5A of the original EH-5. IMO, you rarely will need that much power because for timelapse you are not using FLASH, VR & AF. And Lifeview only occasionally. Skimping on the output power isn't something I would do without more testing on my own ==> bigger battery, more power -- it is just a "handful" but has a price BiXPower-Capacity-Outputs-Rechargeable-Battery
  CAUTION : they mention 9V output but you must read the fineprint (from 9V ~ 12.6V) ==> 9V seems to be the upper limit for Nikon SLR and 7.4V the lower. 12V might fry the camera.
  Similar this 9V-battery may meet requirements most of the times but not in extreme cases. Max output current is 2A instead of 5A : BiXPower-Capacity-Watt-hour-13300mAh-Rechargeable
  .
• converting 12V DC into 7.4V...9.0V DC => NO ASSEMBLY REQUIRED
  There are several suitable converters on Amazon -- and many more on eBay and other sites. Here is one example : Vktech-Converter-Regulator-Power-Module
  I've intentionally picked 7.4V instead of 9.0V (see explanation below) but there also are 12V-to-9V converter.
  .
• Connecting the DC/DC-converter input to the battery
  All that's needed are two wires -- one red and one black -- and match them with the PLUS & MINUS pole of the battery. Details vary based on battery type but the Li-Ion models I have seen use a 2.1mm x 5.5mm Plug (Astronomy gear & CCTV is using the same). For Lead-Acid -- see below.
  .
• connecting the DC/DC-converter output to the camera.
  Since I haven't seen a cheap source for the Nikon DC-plug, my suggestion is to go the "dummy-battery" route. You can enhance this by adding a battery grip (like I did) or by using an imitation EH-5B. The connectors also look like 2.1mm x 5.5mm -- BE CAREFUL not to confuse them with the 12V.
  .

Like David Kingham said, buy the cheapest EH-5 and dump the AC power supply. My approach differed a bit. I've purchased a cheap (vertical) battery grip and add the DC/DC to the inside : stargazer95050/29098819 The "dummy-battery / grip" option has the advantage of powering cameras _WITHOUT_ a DC input plug (and there are many)

• If you want to go the DC-input route, the strategy is very similar and you might even get away with using the same 7.4V DC/DC. The Nikon spec says 9V for that input and there are 12V-to-9V converters available

PERSONALLY, I still prefer the "dummy-battery in grip" approach for one important reason -- fewer external components and all electronic components are shielded from nasty weather. Even simple dew can short a circuit. When you look at my example, you see there is only a single 2.1mm x 5.5mm connector and that is the 12V input. No danger of accidentally mixing up the lower 7.5V voltage with the 12V.

You can choose the "dummy-battery" without the extra grip -- but Nikon didn't have the foresight to include a rubber seal for the DC-cable. Canon has such seals and even the cheap 3rd-party OEM-grip has it. Drilling a hole into a $30 grip is less risky than putting a $1500 ... $3500 camera under the knife.


You can increase the capacity a lot and reduce the price by using a Lead-Acid battery. Size & weight vary, as do the connectors. Don't forget to add a 12V battery charger. In terms of Wh / dollar, these batteries are hard to beat. In terms of Wh / weight, the Lead-Acid are on the loosing side.

The suggestion I outlined above uses a common 12V input (within broad tolerances) and you can choose the right power-/battery-source and still keep the same converter.
In many cases you may even be able to keep the same battery & converter and just swap one "dummy" for another as long as they all are 7.4V (with is quite common)


Picking 12V as the common "rail" / intermediate voltage isn't such a bad idea. Not only do cars use it, it also is widely used in Astronomy and many DIY projects. Chances are, you find more 12V power supplies than for any other DC voltage.



Comparing the DIY against the $$$ PRO-EQUIPMENT
============================================

My challenger is this : www.ipernity.com/doc/315163/29135587
A DIY combo made from a 20Ah 12V Li-Ion battery plus a DC/DC-converter inside a (cheap vertical) battery grip -- and this thing works in my telescope setup.

One popular choice by professionals is the "Vagabond Mini Lithium" with its embedded 12V 8.8Ah battery [www.paulcbuff.com/manuals/vmini.pdf] and given its 120V AC-outputs, the Vagabond is more flexible. OTOH, if you know in advance that you want to power cameras and the like, the Vagabond approach wastes a lot of energy (and thus battery lifetime) by first amplifying 12V to 120V AC only to subsequently reduce the 120V AC down to 7.4V, 9V or even 12V DC -- this choice doesn't require any DIY !! And it also is compatible with any (low-power) equipment you have. The very compact & attractive design of the "Vagabond" with the elegant combination of converter/base-unit and the replaceable-battery are good reasons for its popularity.


The "Vagabond" and similar are multi-purpose devices.
The solution I am suggestion is INTENTIONALLY NOT MULTI-PURPOSE -- by skipping the whole 120V-AC stage, this converter is more efficient and also a lot smaller. You can fit the DC/DC converter into the volume a regular 12V DC-plug (cigarette lighter + bigger plug) would require.
Nevertheless -- 8.8Ah versus the 20.0Ah is a significant disadvantage for the "Vagabond Li". To power a SLR, the Vagabond requires the built-in AC-inverter plus a 120V AC to DC-converter (Camera's AC power-supply).

It is possible to save a lot of power by skipping these high-power up- & down conversions and use a "simple" DC/DC converter to generate 9V (or 7.4V) from the 12V battery. Not only is the converter much, much smaller, also it eliminates the need for bulky 120V AC-plugs. And did I mention the lower price ?? -- the battery ranges from $30...$150 and the DC/DC converter is ~ $10. The Vagabond starts at $240 (plus S&H & tax)




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