This is a very basic diy dummy battery that anyone should be able to make, some soldering and cutting/drilling is required. In case you will also make the dummy battery out of hot glue and use an xacto knife to cut off the excess, then be very careful as one slip-up can cause a bloody mess!
Amazon Affiliate links for this project, it won't cost you more but any purchase you make I might be eligible for some commisson which will help the channel grow.
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Items and equipment for this project:
DC-DC MT3608 converter amzn.to/487fdW4
Plastic box (I used 2.4"x1.41"x0.98") amzn.to/3SVqGnt
Power plug kit amzn.to/4bAc6ZS
Resistor kit amzn.to/4bBI0VU
LEDs amzn.to/3SwYTIx
PCB kit amzn.to/3wjZ16u
Hot glue gun kit amzn.to/3HUd2dF
Soldering kit with Multimeter amzn.to/49taKy7
Stranded wire 24 gauge amzn.to/4bsoKtP
Drilling hobby kit amzn.to/3OFKDfv