Shooting time lapse photography – or very long exposure astro photography, requires a lot more battery life than a single charge on the camera’s regular battery.
We use Nikon D200 and D300s which use Nikon EN-EL3e lithium ion rechargeable batteries. However, there is no good commercial option to use a supplementary external battery.
The approach presented herein would also apply to other DSLR cameras – most of which use a similar battery.
It is possible to use an AC adapter (such as a Nikon EH-5a) to power the camera – but this option has several limitations. It requires either a long extension cord or an AC generator. But that sacrifices mobility. Alternatively, you could use a 12V power source, such as a car battery and a DC to AC inverter. But converting 12V DC (battery power source) to 120V AC (inverter) and back to 7.4V DC (camera adapter) incurs a lot of losses – it is much more efficient to eliminate any conversions and simply use the same voltage battery, with a larger capacity.
The problem is connecting a suitable external battery to the camera. To do this I chose to hack an inexpensive aftermarket EN-EL3e and connect it to a larger external battery. (You could also connect the camera end of an EH-5a adapter to a car battery – but a 12V DC to 7.4V DC adapter would still be necessary, and an EH-5a is pretty expensive to use just for for the connecting socket.)
The Nikon EN-EL3e is rated at 7.4 volts and 1500 mAh. A Canon BP970 high capacity camcorder battery is also rated at 7.4 volts, but 7200 mAh. That means a single BP970 battery (theoretically) holds nearly five times the capacity of a EN-EL3e (1500 mAh x 5 = 7500 mAh). This same approach will work for a Canon 5d or any similar DSLR. The key thing is to match the specified voltage of the proposed external battery to your camera battery – but look for a high capacity model – the higher the milliampere-hour (mAh) rating, the higher the capacity, the longer it will run your camera.
For this project I used:
You will also need a few feet of high gauge wire (I used 28 gauge from an old infra red extender I had lying around) a soldering iron, hot glue gun, phillips screwdriver and a multimeter.
You should probably also know how to solder (its not hard – practice first if you are not sure) and a have a basic understanding of parallel versus series wiring.
The following is a step by step tutorial on two ways to connect a sacrificial EN-EL3e to an external high capacity battery. Taking apart a lithium ion battery is a potential hazard – all batteries warn you to not disassemble them – so do it at your own risk.
Note: Nikon and Canon camera batteries have a built in circuit board that tells the camera how much charge the battery has and controls charging. You cannot remove this circuitry from the sacrificial camera battery – or the camera will think the battery is dead and will not function. If you have a camera that doesn’t have a battery charge indicator, or one that can be turned off – you can simply remove the small circuit board in your sacrificial battery.
Carefully cut open your sacrificial battery along the seams – without damaging the innards.
Separate the two halves. Components of the battery may be taped to the plastic cover, so be gentle.
Identify the circuit board at the terminal end of the battery. Note the positive (B+) and negative (B-) inputs to the circuit board from the battery cells. The common connector (VC) is part of the safety and charging circuitry. The outputs from the circuit board centre (C), positive (P+) and negative (P-) are connected to the corresponding battery terminals.
Identify the lithium ion battery cells and carefully remove them from the circuit board.
Remove the circuit board from the terminals (Note: At this point I proceeded to remove the entire circuit board and connect the wires directly to the terminals. It wasn’t until I put the whole thing together and tested it that I realized that the circuit board has to stay. So I put it back).
Remove the terminals from the battery case (this is not necessary if you are good at soldering and are not worried about melting the case).
Solder new leads to the terminals.
At this point I put the battery back together without the circuit board. However, as noted – the camera didn’t work, so I had to splice the circuit board back in.
Here the battery terminals center (C), positive (P+) and negative (P-) are connected to the corresponding terminals on the circuit board. The external battery leads are connected to the positive (B+) and negative (B-) circuit board inputs. The common safety/charge control (VC) is left unconnected.
Components held in place with hot glue (do not use silicone – it is corrosive and will kill the circuit).
Sacrificial battery re-assembled.
After finishing this battery, I decided to do another one with a slightly different approach. Instead of removing the lithium ion cells from the sacrificial battery, I left them in place and just connected the leads from the external battery directly to the terminals of the sacrificial battery in parallel (positive to positive, negative to negative). This keeps all of the original circuitry intact and also provides a 7.4V battery with a total of 8700 mAh (7200 mAh from the external battery plus 1500 mAh from the original cells). In hindsight, it was quite a bit easier.
External positive (+) and negative (-) leads from the external battery connected directly to the positive (+) and negative (-) terminals on the sacrificial battery.
To hold the external battery I used a compatible baseplate. This way the external battery can be easily removed from the system for charging.
Unscrew the baseplate and separate the two halves. Remove the connecting wires.
Connect the positive (+) and negative (-) leads from the external battery to the positive (+) and negative (-) terminals on the baseplate (you might want to remove the terminals first if you are worried about melting the baseplate components).
Re-assemble the baseplate.
Connect a charged external battery to the baseplate and check the voltage from the terminals on the sacrificial battery. Make sure you haven’t reversed the polarity along the way. In this case the external battery is reading 8.27V even though the battery is only rated at 7.4V (this is normal as a fully charged battery will have a slightly higher voltage than a depleted battery). If somewhere along the way the safety mechanism in the sacrificial battery’s circuit board has been tripped, you may get a reading of zero volts. However, the safety should re-set after a period of time. (This happened to me – I went out for dinner and when I got back it was working again.)
Fully charged genuine Nikon EN-EL3e battery reads 8.11V.
Place sacrificial battery into the camera.
Close the camera battery door. The wire I used is small enough, and there is enough play in the battery door that I can close it without having to modify the actual door. You might have to notch out the door if you can’t get it closed – the camera will sense that the door is open and won’t work unless the door is firmly closed.
Connect the external battery and turn the camera on. For some reason, the system with the sacrificial battery cells removes shows just shy of full power. The system with the external battery leads connected in parallel shows full power.
Full power and ready to go with four to five times more battery capacity.
If a single 7200 mAh external battery isn’t enough for your requirements – you can also connect two together in parallel for 14400 mAh (or more – within reason).
Any questions – hit me in the comments. Cheers!
Time Lapse Photography and Video Production
Toronto, Ontario, Canada
905 818 5711