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.

Materials

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

Tools

Cura or similar splicer

Grinder

Drill bits 1 mm and 8 mm to 12 mm

Hand or low speed drill

Pliers

Cutters

Soldering Iron

Solder

Round profile needle file

Flat profile needle file

Sanding paper

Wire wool

Scalpel

Protective Glove

Eye Protection

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.)

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.

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.

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.

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.

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

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.

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.

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.

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.

Hope you found this informative and interesting.