January 31, 2009

HOW TO: 9V Battery Safe

I originally wrote this post on my other blog (now retired), but thought it was worth bringing over. In today's How To, we'll be teaching you how to create a small, little safe out of something you probably never thought of: a standard 9v battery. The finished product is only slightly lighter than the original, and unless someone is looking very closely, you cannot tell the difference visually. For safeguarding your valuables, this is last place a person would think to look.

It's easier to make than you think, and since you probably have most of the required materials hanging around the house, you can't beat the price. While I don't claim to have come up with the idea, I've added a couple features that I feel make this the best 9v battery safe that your average hobbyist can make.

Cheesy Legal Warning: If you get hurt attempting to make this, use it, or get busted for doing something illegal with it, it's your responsibility. While I can't foresee any real danger to this project, I know someone will "accidentally" swallow the battery and want to sue for stomach upset. Also, all text, photos, and material are copyrighted by me, so no stealing (though linking to this blog is highly appreciated).

All right, let's get to it!

Required Materials: 1 9v Battery
Epoxy, Gorilla Glue, or JB Weld
Q-Tips (to mix/apply epoxy or glue)
Metal File
Sharpie (for marking)
Wire Cutters
Needle-nose pliers
Small flathead screwdriver
Stock metal (any kind, approx. 1/8 or 1/16 thick)
Measuring tape or Calipers

Your materials should look something like this:

Now that you've assembled everything, we'll start by flipping the battery upside down and prying open the two tabs (it's on the side of the battery that has the crease running down it.)

As you get the tabs open, you'll want to cut a slit on the corners to allow you the bend the tabs down without bending the rest of the metal.

You'll now want to fully bend both tabs down just enough so that you can see the layer of plastic that makes up the bottom of the battery. With your needle-nose pliers, grasp the end of the plastic and pull it straight out.

Cut the plastic shell that wraps around the internal unit to create access to the layer beneath. Don't worry, this kind of battery won't leak just by cutting this shell.

Now just remove the internal paper liner with your needle-nose pliers like you removed the plastic bottom earlier.

You'll now need to pry one of the metal ridges on the side up so that you can pull out the individual cells later.

Now you can finally remove the individual cells from inside the battery.

Remove everything from inside the battery. You should wind up with 6 cells, the plastic shell, another paper liner, and the contact points.

We'll need to clean up the edges of bottom of the battery and reshape the side metal ridges that we bent earlier. Cut off the metal tabs that you bent down in the beginning and bend down the side ridges until it looks something like this:

Now comes the trickiest part: creating the spacers. These will be glued on the interior sides of the battery so that we can create a sliding door that opens and closes the hidden compartment. The exact sizing of the spacers is CRITICAL! If they are not tooled correctly, they will either not support the plastic battery contacts piece or they will let the bottom compartment cover slide out by itself. Use careful measurements and a metal file to obtain the perfect fit.

The most critical part of the spacers is that they are relatively flat, are spaced relatively close towards the bottom (but not touching, as the compartment cover needs space to slide), and have enough surface area with which to be glued. Another important feature is that they must be about as long as the battery is, so that it will support the battery contacts when you go to reassemble it.

Now we need to apply the bonding agent. You can use gorilla glue, JB Weld, or others products, but I decided to go with an epoxy. With epoxies, make sure you mix both agents thoroughly before use or you'll end up with weakened adhesion. You'll notice I didn't cover the whole side with the bonding agent; it's so that it won't spread into the sliding compartment and jam up the cover.

I recommend using Q-tips to apply the bonding agent, as this deposits cotton fiber into the mixture. This actually helps the agent to cling more securely to the two surfaces. To prep the battery, make sure the battery contacts (the piece of plastic that contains the battery terminals) are properly situated. The spacers will be inserted, and if they are sized correctly, they will support the battery cover piece. After the agent is applied, insert the spacers into the interior sides of the battery.

At this point (before the bonding agent sets), we want to check for three things:

1) That the spacers properly support the battery contacts.

2) That the spacers sit flush against the interior walls.

3) That there is enough room for the plastic bottom piece to be re-inserted, but not so much room that it falls out by itself.

If any of these conditions are not met, the spacers must be retooled. (Just wipe off the glue and try again. You didn't let it dry, right?) If everything looks good, then we can proceed. Stuff a paper towel wad inside the battery to provide pressure between the spacers and walls of the battery. Then, insert the compartment cover piece halfway so that the spacers don't shift and block the spacer from being inserted later. Allow to dry for whatever your bonding agent has recommended.

After it has dried, remove the paper wad and cycle the compartment cover piece a couple times to make sure it works correctly. If you did it right, the cover will securely hold your valuables in place, but can still be easily opened by using your thumb to slide it back. After you create a couple, making these safes becomes relatively easy.Finished product! I certainly hope you've enjoyed our first how to. It won't be the last.

Happy Hacking.


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