Nikon EN-4 Battery Lithium-Ion Conversion

I used to have two Nikon D1-series cameras – a Nikon D1 and a D1X. These, along with the D1H, were the first Nikon pro-level digital cameras – essentially Nikon F5 bodies with digital innards. These cameras were powered by the Nikon rechargeable nickel metal-hydride (NiMH) EN-4 battery.

Large and heavy, these batteries were also infamous for not keeping a charge after they have been used for a while. They were a bane for photographers using the D1 series cameras as they had to carry 3 to 4 of these heavy batteries on a photographic outing as these batteries were, on an average, good for about 300 shots each.

That was 20 years ago, the D1 series have long been superseded by newer models of Nikon pro-level digital cameras – D2 series and the latest of the pro-models, the D5. Nikon, cognizant of the shortcomings of the NiMH batteries, replaced the batteries of the new models with more reliable lithium-ion (Li-Ion) batteries.

I recently bought a 2.7 megapixel Nikon D1H camera on eBay for $50. $50 is a cheap way to shoot with a pro-level Nikon camera, albeit 2.7 megapixels. It came with 2 Nikon EN-4’s and 1 after market EN-4. One of the Nikon EN-4’s was dead – the charger couldn’t revive it anymore. I had seen another seller on eBay offering a Nikon D1X with a Li-Ion converted EN-4 battery. First time I had seen one of these and it looked like a good way to extend the shooting stamina of the D1H. I decided to play Dr.Frankenstein and revive the dead EN-4 that I had!

Scouring the internet, I came across a few posts describing how these batteries could be converted. The EN-4 could be configured in different ways but fundamentally the NiMH batteries in the plastic EN-4 casing had to be replaced with two 18650 Li-Ion batteries. 18650 batteries are so called because they are 18mm in diameter and 65mm in length. Each are rated at 3.7V with varying capacity (mAh) depending on the manufacturer. The Nikon EN-4’s were rated at 7.2V and 2000mAh. Two 18650 batteries will provide 7.4V which is enough to power the D-series Nikon cameras.

So I set out to buy the 18650 batteries and charger on Amazon. I settled on 4 Samsung 18650 Li-Ion batteries rated at 3.7V and 2500mAh each. While I waited for the items to arrive from Amazon, I started disassembling the EN-4.

Using a Stanley knife, I started scoring along the joint lines of the EN-4 casing on the sides, being careful not to cut myself. After scoring for about 15mins, I could start seeing the blue NiMH batteries inside the casing.

Finally able to open up the casing by cutting across the battery compartment, the NiMH cells were exposed. The NiMH cells (six of them) were stuck firmly to the casing with double sided tape. Needed to remove those slowly.

The six batteries are connected in series. To unravel the battery arrangement, I cut the black wire near where it is soldered to the last cell at the negative end of the series.

The six NiMH cells arranged in a line on their series connections. The cut black wire (on the left) is connected to the negative terminal of the EN-4 battery pack. The other wire is connected to the charging socket of the EN-4 battery pack. I left this alone.

Next I set out to disconnect the piece of metal strip soldered onto the positive end of the cell series. This was corroded (white corrosion) as seen above, rendering the EN-4 battery pack dead. Interestingly, despite this first cell being dead, the remaining five battery cells were each carrying an approximate 1.2V charge.

I slowly scraped off the corrosion and cut away the micro-solders of the metal strip from the cell. This metal strip will serve later as the positive terminal connection of the 18650 Li-Ion cells.

After cleaning up my work space, I am left with 2 halves of the EN-4 battery shell. This will form the “battery holder” for the two 18650 Li-Ion cells.

While waiting for the Samsung 18650 Li-Ion cells and charger to arrive in the post, I decided to disassemble a “dead” Nikon EN-EL4a Li-Ion battery pack that I had. The following day embarked on opening up the EN-EL4a.

Removing the Li-Ion cells from the EN-EL4a casing was much more difficult because of the tight space within this compact battery pack. Lo and behold, there were three 18650 Li-Ion battery cells in a EN-EL4a pack giving it an 11.1V 2500mAh rating, as I suspected (3.7V x 3).

Like the EN-4 battery that I disassembled, one of the three Li-Ion batteries was dead while the other 2 still carried a charge. By this time, the 18650 battery charger had arrived but the Samsung batteries were still a couple of days behind. I charged the 2 that still carried a charge and fully charged they carried about 4V each.

With the 2 Nikon 18650 cells at hand, I started on completing the project.

First I removed the springs and backing from a couple of AA cell holders. These will serve as the connectors for the 18650 cells in the EN-4 casing.

Soldered the previously cut black “negative” terminal wire from the original NiMH cells to an AA spring and its backing (cut to fit in the EN-4 casing). This wire is connected to the circuit board of the EN-4 battery pack which I did not disassemble.

This backing with its spring is then glued to the EN-4 casing forming the negative terminal. The metal strip that was disconnected from the “corroded” positive terminal of the NiMH cell series forms the positive terminal. This metal strip is also connected to the circuit board.

Throughout the project, I kept on the white terminal plastic cover of the EN-4 casing as much as possible to protect the small protrusion at the end of the casing from breaking accidentally. This small protrusion deactivates a switch in the camera battery chamber. If this is broken, the switch is not deactivated and the battery pack will not work.

The Nikon Li-Ion 18650 battery cells are placed in the EN-4 casing to check the position for the connecting board on the other end.

I cut two 16mm diameter wood dowels to form the base support for the cell connecting board. The board is made up of the plastic backing from the 3-cell AA holder with one spring for the negative end connector and an aluminium metal strip constructed from a Diet Coke can to form the positive end connector.

Each dowel has 2 grooves cut into the base to accommodate plastic protrusions on the inside of the casing. The connecting board fits perfectly between the plastic protrusion (to fit the bottom screw of the EN-4 cover plate) and the adjacent plastic divider in the casing.

This cell arrangement provided 7.86V, higher than the NiMH EN-4 rating of 7.2V. However, this apparently is still safe for the camera circuits from my research on the internet.

Before glueing the pieces together, I tested this battery pack in the D1H. Carefully inserting it into the battery chamber of the camera and turning it on, both top plate and back LCDs show their customary readings and the monitor reads as normal. More importantly, the shutter fires! Hooray!

Taking the pack out from the camera, the dowels and backing are then glued into position with super-glue.

The electrical connection on the board is formed by connecting the aluminium strip to the spring. This worked fine before glueing the strip to the board but once I glued the strip, the connection no longer worked. I surmised this was due to super-glue creeping up between the metal strip and the spring by capillary action and forming a thin “insulating” barrier when it hardened. To restore the electrical connection, I later had to solder in a connecting wire. In future, I would use a small round head screw, screwed to the dowel through the board as the positive connector and connect this to the spring by wire. No glue.

Once the components were glued in position and electrical connections restored, the top half of the casing is readied for re-assembly. Because the 18650 Li-Ion cells are slightly wider in diameter than the NiMH cells, the top half of the casing cannot fit back without removing the sides of the top casing to expose the Li-Ion cells. Once this is done to measurement (and covering the dowels for esthetics), the halves are glued together.

The finished product with the Nikon 18650 cells inserted.

The Franken Li-Ion EN-4 next to another dead Nikon NiMH EN-4.

The Franken EN-4 weighs approximately 150 grams compared to the original EN-4’s 250 grams. Approximately 100 grams less.

Li-Ion Franken EN-4

With the new Samsung 18650 cells and a combined total of 5000mAh of capacity – this Li-Ion Franken EN-4 battery pack has more capacity or juice to last longer and take more photos than the original NiMH EN-4.

Overall, a satisfying project to revive an old $50 Nikon pro-level camera.

4 thoughts on “Nikon EN-4 Battery Lithium-Ion Conversion

  1. Thanks for the inspiration. I had everything laying around so I ran with your idea. I don’t have the Nikon charger so I used springs for tension and made the batteries removable so I can charge them with my $5 charger! I can send a few photos if you would like. Thank you for helping make my old Nikon useable again!

    Liked by 1 person

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