Cord to Cordless Circular Saw Conversion From 100v to 18V

I'm afraid of the used electric power tool with aluminum case, because I used to see one of my power tool that the previous owner install the power cord not correctly. He confused the earth wire with the natural wire. He connected the two wires together, that is so dangerous to test this kind of used tools without checking it first. You can check is here    • Shocking Angle Grinder Restoration  
For safety, including modernization, I decided to convert this tool from electric to battery circular saw powered by 18V Dewalt battery.
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!!! I'm sorry for the mistake if I did in this video !!!
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