Restoring a 1950 Swedish Switch Lantern with a NiFe Battery
In this video, I restore a 1950 Swedish switch lantern — a handheld railway signal used by track workers to communicate and manage train movements. What looks like a simple lantern turns out to be a surprisingly complex and overengineered mechanism inside.
Behind the steel housing there are dozens of parts: mechanical linkages, a color-switching system, seals, structural reinforcements, and an original NiFe (nickel-iron) battery system built for dependable field use.
One of the most interesting parts of this project was reviving that NiFe battery. Unlike modern batteries, nickel-iron cells are known for their durability and exceptionally long service life — but bringing one back after decades requires careful cleaning, proper electrolyte preparation, and controlled testing.
I will now describe the step-by-step restoration process of this NiFe battery:
1 – I began by cleaning the terminals with warm water, carefully — without shaking, hitting, or moving the battery aggressively. The internal elements are quite old and can be affected by shocks.
2 – I carefully removed the caps, as gases may have accumulated inside. The alkaline solution can splash out and it is very harmful, so always wear proper protection.
3 – I drained and measured the electrolyte inside to determine the correct refill quantity.
4 – I flushed the battery with distilled water several times, until no more deposits were visible in the drained liquid.
5 – I then let it dry at room temperature for 48 hours. After that, I measured the resistance (in ohms) to check for internal short circuits. If everything looks good, the process can continue.
6 – I prepared a new alkaline solution using potassium hydroxide (KOH) mixed with distilled water at approximately 20% concentration — depending on the battery type.
7 – I filled each cell with the alkaline solution just enough to cover the internal elements. It is important to leave space at the top, as the solution will start to boil during charging and gases need room to expand. Always work in a well-ventilated area.
8 – I left the battery with the alkaline solution inside for 24 hours to allow it to settle and stabilize.
9 – I began charging the battery. Initially, I used a low current of around 200–300 mA, then gradually increased it depending on the battery’s capacity, up to about 1A. The voltage should be between 3.2V and 3.5V.
At the beginning, I observed a sudden rise in voltage to around 2.3V–2.5V, but as charging continued, the battery stabilized and the voltage gradually decreased. It is recommended to monitor the charging process carefully — both by measuring voltage and by checking the battery temperature, as it can heat.
Restoring the electrochemical side of this lantern was just as important as rebuilding the mechanical mechanism.
In the video you will find:
• Complete disassembly
• Sandblasting and corrosion removal
• Machining new parts on the lathe
• Rebuilding the internal switching mechanism
• Electrostatic powder coating
• Restoring the original NiFe battery system
• Careful reassembly
• Functional testing
The internal construction reveals a level of mechanical overengineering rarely seen today. It wasn’t just a lantern — it was a precision signaling tool built to work in real conditions.
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