I have been searching on Instructables for a cement battery but couldn't find one.This I found very surprising so I can only assume I missed it(if you know of one or more,please let me know).
For now though lets just assume this is the first one and get started with the instructions. I won't post the instructions to the Magbot pendulum itself because you can find that in one of mine other instructables:

Here's one of my other cement batteries running a Magbot Pendulum.

Step 1: Step One:materials and Tools

These are only the materials you need to make the battery.

-Cement or concrete mix
-Aluminium soda can (but other Aluminium can,pot or vessel work too)
-Copper wire (or tubing,rod and sheet)
-Wires or clip leads
-Bolt with two nuts

-Drill(or sharp item to punch the can)
-Tin snips or rotary tool
-Sanding paper
-Something to stir the cement mix
-Small spoon

Step 2: Step Two:prepare the Can,add the Cement Mix and the Copper Electrode

Remove the top of the can,within the rim.Use the the tin snips for this or the rotary tool for a smoother finish.
Sand the inside of the can,then rinse it out.
This one shouldn't be too difficult:add water to cement or concrete mix and stir well till you get a nice thickness.
(You can also put the mix in the can,little amounts at the time then add the water as you go along.I found that this is much cleaner and you also aren't left with leftover cement.)
Get the can(or whatever else you've chosen)and pour or scoop the mixture into it.You can hold on to the piece of metal you choose for the electrode and pour the mix around it.Or(much easier)push in the electrode after you've poured the mix.Let this set or cure till it is hard.

Step 3: Attach Your Battery to the Magbot Pendulum/Joule Thief

Step 3 is the exciting part:attach your battery to the Magbot pendulum and watch it swing into motion(if all goes well).
Most cement batteries seem to be generating about 1.2 V.Some people add other things to the cement as well like:
Alum,Magnesium Sulfate(Epsom Salts) and other kinds of salts,just check YouTube)
Other uses for your battery could be:
-powering a Joule Thief.The circuit in the video I found on Quantsuff's page:http://www.quantsuff.com/LED2.htm .
He is also a member here:https://www.instructables.com/member/qs/ 

-running a pulsemotor
Cement is the last thing i would of thought to use to make a battery! how long does it last?
I haven't tried that out yet,some people had their batteries running for months though.

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More by Brosiman:Cement battery powered Magbot pendulum/Joule Thief Queen Wilhelmina's Light Theremin* Mr.Philips,a Joule Thief robot 
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