Hidden Power




Introduction: Hidden Power

Power may reside in a secret and therefore you may wish to keep it in a safe place and what better than a place of power storage, a battery.

This project will describe the process of converting a battery into a secret storage compartment with the added bonus that it can be inserted into a multi cell battery pack which will still function although with a reduced voltage.

Choose wisely an application that is not voltage critical and no one will be the wiser unless they dismantel the battery pack or measure the voltages.



3D printer

PLA+ filament (Black)

22 SWG (~0.711 mm), tinned copper wire

Battery (AA type)

Multi purpose glue

Black Paint or Black marker and clear lacquer/paint

Epoxy filler

Adhesive Tape


Cura or similar splicer


Drill bits 1 mm and 8 mm to 12 mm

Hand or low speed drill



Soldering Iron


Round profile needle file

Flat profile needle file

Sanding paper

Wire wool


Protective Glove

Eye Protection

Step 1: Preparation

Obtain an exhausted battery, in this case an AA type alkaline. (Other battery types could be used.)

If your unsure whether is exhausted, ideally test it under load to determine its condition.

For example it may not power your torch but has no trouble powering a TV remote.

In the absence of specific test equipment to verify its condition when its no longer capable of powering a Joule Thief or similar low power circuit we can consider it exhuasted.

We want an exhausted battery in order to prevent the occurance of a short circuit resulting in damage to the blade from an electrical discharge when the blade contacts the central negative pin and the positive outer case. Even these small batteries are capable of a large current of several amperes which can create a lot of heat.

Better still use a grinding wheel which is none conducted and exposes the end rather than cutting into the battery.

Further details for the type of battery used in this project can be found in the attached document.

(No affiliation or connection with the manufacturer of the product in this project, details provided for information only. Check with the manufacturer for the latest updates.)

Step 2: Removing the End Cap

With a scalpel carefully cut off the plastic cover that curls around the edge of the battery.

This will expose the edge of the end cap that is spot welded on the end.

With a flat blade screwdriver slip this under the edge of the end cap and carefully pry it off.

In the process the end cap may bend a little but if not too extremenly bent can be flatterned back into shape.

This will expose the vent and insulator ring.

Now with these removed the end can be ground off.

Step 3: Grinding

Wearing suitable gloves, eye protection and any other relavant precautions related to the equipment to be used and the process to be carried out.

Carefully proceed to grind off the negative end of the battery.

You will need to remove ~2 mm of the main body to expose the inner construction.

The central ring is the anode pin.

The white ring is the anode element.

The dark ring is the cathode element.

The next stage is to remove these elements from the body.

Step 4: Active Elements Removal

Wearing suitable gloves and eye protection.

Consult local regulations for the disposal of batteries to be used.

Wrap the battery with a cloth, bubble wrap, antislip material, cork wrap or other suitable material to protect the battery from being crushed when held in the vice or clamp and to prevent it slipping and marking the external surface.

First remove the anode pin with a cocktail stick, a pair of pliers or tweezers which should just slide out.

Next with a hand drill or electric drill on a slow speed, starting with an 8 mm drill bit remove the white anode paste.

The white paste is very soft and will come out easily.

Next proceed with a 9 mm drill bit to remove the dark brown cathode material, this is much more dense than the white paste and a little more difficult to remove.

Progressively, increase the drill bit to 10 mm, 11 mm and finally 12 mm which will remove all but a thin layer at the circumference of the cylinder.

This thin layer can be removed with flat blade screwdriver and/or scalpel blade.

The edges of the cylinder will be sharp as a result of the grinding process and will need to be smoothed with sanding paper or a round profile file.

Application of wire wool wrapped around a stick and pushed in the cavity should remove any remaining active material adhering to the insides.

Once all the active material has been removed clean out the interior with soap and water whilst using a cloth or tissue to clean out any residues. Then dry with a cloth or tissues.

Having now cleaned out the active material the next stage is to fabricate the interior capsule.

Step 5: Secret Capsule Design

The secret capsule is designed using BlocksCAD and then 3D printed.

The design requirements were:

1: Fit in to the battery case cylinder and include the missing 2 mm to ensure its the same size as a battery of the same model, type and size.

2: A cavity to hold the item(s) to be hidden.

3: Have a compression split to allow the capsule to grip within the cylinder and accomodate minor size variations.

4: Allow a connection from the negative to the positive terminal via the end cap and an internal wire that makes contact to the cylinder body when the capsule is inserted.

Once designed the STL file is generated and loaded in Cura for preparation to 3D print.

Step 6: 3D Print Preparation

Using Cura to generate the Gcode file with the following settings.

Layer height - 0.15 mm

Infill Density - 100%

Infill Pattern - Cubic

Build Adhesion - Brim

Print time ~48 minutes

Weight ~4g

Printed with PLA+ black filament

Step 7: Post Processing

Remove the brim

Lightly sand the exterior of the caspule to flattern the layer lines to make it easier to slide this in and out of the battery body.

Lightly sand the top end of the capsule that will sit behind the positive terminal making sure its the correct length when fully inserted and the end cap is in place. Either by measurement or direct comparison to another battery of the same model, type & size.

Make a 1 mm hole in the centre at the negative end.

If necessary, clear out; the two side holes along the wire channel.

Its now time to make the electrical connections.

Step 8: Wiring

Using 22 SWG tinned copper wire place a small bend in the end and insert this into the lower side hole in the wire channel (closest to the negative end).

Push this forward and it will just protrude through the centre hole at the negative end.

With pliers pull 20 mm of wire through the hole whilst pushing at the entry hole.

Solder the end of the length of the visible 20 mm to the back side of the end cap.

Push the wire back through the centre hole whilst pulling the excess back through the side hole.

Prior to fully seating the end cap apply a little glue to its back then take up any slack so it sits flush with the end of the capsule.

Bend the wire eminating from the side hole and bend it to sit along the channel.

Pulling the wire tight bend the wire into the capsule and out through the hole near the top, bend at a right angle and cut ~5mm from the hole.

Step 9: Fill the Gap

The wire in the channel and the gap between the end cap is filled in with epoxy filler.

Apply tape around the main body of the battery aligned with the cut edge to protect the surface and apply the epoxy to the gap.

Once set carefully sand or file the epoxy to align with the main body of the battery.

Only having grey filler I coloured this in with a black permanent ink pen and and painted this with a clear laquer for a matching finish.

Remove the tape.

Step 10: Incognito Mode

Now is the time to hide your item(s).

Pull open the capsule place the item(s) to hide inside the capsule and slide back into the battery body.

For additional camouflage mix with other batteries or substitute with a functioning battery in a battery pack for an appliance thats not compromise by a reduction in voltage.

In this case an LED lighting string was used, with the hidden capsule battery in the centre of the battery pack.

Step 11: Finally

Hope you found this informative and interesting.

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    5 weeks ago

    Aside from this being less dangerous, would it not be easier to score a thin line length-ways across the battery (just into the plastic wrap) and unroll the plastic cover off the battery, and then just wrap that over a 3D print that is the same size as the battery? On some cheap batteries you can easily unravel the plastic skin cover by hand! Then you can avoid battery acid and properly dispose of the battery in a recycle facility. The cut seam of the outer wrap will can be easily hidden away from the viewer, hidden against the object case.

    You can also buy 5 fake AA batteries for 0.66cent that are already hollow and have a pass-through cable.

    fake dummy battery.PNG

    Reply 5 weeks ago

    Thank you for taking the time to comment. I am asked many times by people why I choose to make anything when I could likely buy it, put simple I enjoy it. Whether the projects take hours, months or years. The easier option would have been doing nothing, saving both time and money. However, your suggestion is another alternative people can consider in deciding which direction to take.


    Reply 5 weeks ago

    Did you bother to read the start of my comment? I suggest an alternative that is much safer. You can still 3D print the inside, but you don't need to waste hours taking the inside out, you can just remove the cover and put it over a 3D print. I never said don't make things, I said don't be dumb and post dangerous ways of doing something when there is a safer DIY alternative. Messing with battery chemicals is dangerous. You just don't want to admit there is a smarter easier DIY solution.


    Reply 5 weeks ago

    I have to agree. You are playing with things that may very well have a negative impact on your health down the road. and trust me, I come from a generation that did not have the benefits of todays knowledge and case studies. A simple 3D printed tube, or even a suitable alternative cylinder with the removed wrapper of a battery is far safer. I would think there is even a way to print a very good likeness of that wrapper as a sticker, with todays materials and technology.


    Reply 5 weeks ago

    Yes these fake batteries are a great option for those of us who don't have a 3D printer. They don't exactly appear to be "fake" batteries, as they do not look real at all. They seem to be some type of Battery spacer or by-pass. My guess is that a very enterprising aftermarket battery company wants to sell (for example) one rechargeable Li battery that has the same output as 2 or 3 standard batteries linked together in series. These things, which are not made to look real, literally just fill in the gaps so that one modern battery can now do the work of 2 or 3... I have never seen these, but that is my best guess.
    Combined with the other elements of This instructable, they would then hopfully look real.


    Reply 5 weeks ago

    Thank you for taking the time to comment. I am asked many times by people why I choose to make anything when I could likely buy it, put simple I enjoy it. Whether the projects take hours, months or years. The easier option would have been doing nothing, saving both time and money. However, your suggestion is another alternative people can consider in deciding which direction to take.


    5 weeks ago

    This is so cool! Wish I had known it when I was cheating in elementary school exams.


    5 weeks ago

    I will use this for the plans of the new submarine technology.


    5 weeks ago

    Impressive. I can and will use this information. I just need a 3d printer...


    Reply 5 weeks ago

    Thanks. An alternative would be to turn a length of wood, perspex or other suitable material into a cylinder, drill out the centre and cut out the side. However, this assumes you have a lathe or converted drill. I did find PVC pipe with a 13 mm OD in white, other colours may exist, just need to cap the end and cut a slot, this is another option to consider. sourcing map PVC Pipe Round Rigid Plastic Tube 11mm ID 13mm OD 500mm White for Water Pipe,Crafts,Decoration,Cable Sleeve 2 Pack : Amazon.co.uk: DIY & Tools

    WhiteWolf McBride
    WhiteWolf McBride

    5 weeks ago

    Better than using an unmarked section down the end, if you can find a color change along the body. You use the top half of one battery, and the bottom of the other, to make the body seam almost imperceptable where a label coloring change occurs. On that Duracell, either above or below (or somewhere in the middle) of that blue metallic band. A different brand may give you a better point to make the seam (perhaps a rechargeable?)


    Reply 5 weeks ago

    Thanks for the comment, The two battery option matched at a seam would certainly work.


    5 weeks ago

    Great idea, I'd almost suggest doing this with a going to a D, or 9V the internal size would allow for more space, and easier fabrication of the inner sleeve if you didn't have access to a 3d printer.


    Reply 5 weeks ago

    Thanks, agree with a larger battery. However at the time only had an exhausted AA battery to hand and did not what to sacrifice a functioning battery of a larger size.