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I'm pursuing a DIY project, creating a memory box for The Eras Tour that had LED wristbands. In said wristbands are 2 CR2032 (3V, 0.2mA) disk batteries on square metal plates connected by a metal bridge on the backside of the batteries. I wish to discard the batteries, as I do not want to take out the pull tab each time I want it to be on, nor to replace the batteries in the future. So what I want to do is to make a relatively simple circuit, merely a cathode and anode connected to a power outlet. I do have two wristbands I would like to connect.

So I require your help on what is the best way to go about this. I would like to have them connected to either a power socket (in the Netherlands, 230V) or USB-A (to a powerbank). Do I connect them in series or parallel? How do I transform and reduce the voltage and amperage to a safe level? Any components you can recommend, I'd happily buy. I can access a soldering machine at my university if needed.

Thank you for your help! Kindly, Lex

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    \$\begingroup\$ You need to figure out if a wrist band with two batteries has the batteries in parallel (3V) or in series (6V) and then determine what is the load current from the battery and how much the battery voltage is whem loaded. Some simple devices just short circuit a LED directly to a weak battery in the hopes that the LED does not burn out. So don't expect the LEDs to survive when connected to another type of voltage source. \$\endgroup\$
    – Justme
    Commented Aug 1 at 11:03
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    \$\begingroup\$ In what way did they light up? Constantly on till the batteries ran out or somehow synchronised with each other? The ones Coldplay use respond to commands sent by IR so they wouldn't do anything unless you could replicate those commands. \$\endgroup\$
    – Finbarr
    Commented Aug 1 at 14:25
  • \$\begingroup\$ @Justme yes, they are in series, I didn't make that clear at first. I will try hooking up a 5V USB source, so keeping my hopes up not to short circuit, hahah. \$\endgroup\$
    – Lex Plantenga
    Commented Aug 1 at 23:00
  • \$\begingroup\$ @Finbarr They have an 'idle' mode when not directed by IR (they lit up similarly to Coldplay, too), so in bursts of a second on, then off, then on in a different colour, etc. Luckily I don't have any reprogramming to do that way :). \$\endgroup\$
    – Lex Plantenga
    Commented Aug 1 at 23:02

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If the "metal bridge" is not connected to a circuit board or wire, then the batteries are probably in series. The series pair would supply about 6.4V when new, and 5.0V when nearly discharged. There's a good chance a simple USB 5V supply could be used as a substitute in your memory box. You'd have to cut off the cable end, strip the wires, confirm which ones give + and - 5 volts with a multimeter, and solder them to the metal plates that were the battery contacts. If the metal plates aren't solderable, though, you'd have to improvise to force the wire against the plates (spring? foam? tape?).

You're not going to wear the bracelet while it's energized this way; otherwise there might be some safety concerns.

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  • \$\begingroup\$ Hi Mark, thanks for the 5V USB supply suggestion! Yes, sorry, metal bridge didn't make sense, it is just a 'wire' connecting the batteries in series. The metal plates should be solderable, so I wll do so when university open backs up again. Thanks for the help! PS: yes, the bracelets won't be worn when in use, haha. They will be mounted to a display case. \$\endgroup\$
    – Lex Plantenga
    Commented Aug 1 at 22:57

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