One of the more annoying types of battery used in small electronics such as electronic shelf labels (ESL) is the double coin cell with a cable, such as the CR2450-2P. Instead of having battery terminals inside the ESL, it comes with a JST-style port that the battery pack plugs into. The battery pack is nothing more than 2 CR2450 coin cells welded together with wires and a matching JST plug, inside a heatshrinked foil. These packs are incredibly expensive compared to just buying loose CR2450 coin cells from the brand of your preference. I happened to run into these packs with the 3.5″ Solum M3 Core ESL which I was going to use for OpenDisplay. Very frustrating.
But the nice thing about the CR2450-2P is that they’re not actually putting the 2 cells into series, adding up their voltage. They’re connected in parallel, which means there’s just more power stored in the pack than in a single CR2450 cell. But it also means that it becomes trivial to replace the battery pack with a normal single coin cell, as long as you accept that the single cell will give you half the battery life of the pack! You will need a battery pack to dismantle, as you’ll reuse the wires and plug.
Take your Solum tag and pop the back off using a screwdriver or other tool.
Detach the battery pack from the ESL. As you see, in my case it’s an Omnergy CR2450-2P battery pack.
Use scissors to cut open the heatshrink. Be careful though! You don’t want to accidentally cut the wires. Start at the bottom, and preferably on the back side where only a welded bridge sits. Slowly cut upwards until you can free the batteries from the foil.
This is it! Ridiculous right? Just 2 bridges and some wires welded to 2 coin cells, and you pay a 5x premium for that. As you can see, the red wire goes to the positive side of the coin cell and the black wire to the negative side. Remember that for when we put it back together!
Use needle-nose pliers to pull the black wire’s connection plate away from the battery. What worked best for me was to slide the plier under the plate, all the way up to the weld-point from the direction of the wire, grab the plate tightly, and then rotate it clockwise against the cell to pull the weld off. Repeat for the second weld lower down and detach the plate.
Repeat for the red wire. Now that you have detached both wires and their plates from your battery pack, you can dispose of the coin cells as you would any other battery. The plug and the wires is all you needed. You’ll have deformed the plates pulling them off the batteries, so flatten them out by squishing them with the plier, as you’ll want them to be as flat as possible for the next step.
Time to replace the actual battery! Take the red wire and use some adhesive tape (yes, sorry, I’m fully aware that this is not the correct way to attach wires, but I also don’t really care in this usecase) to tape the red wire’s plate to the positive + side of a new CR2450 coin cell – I really like the Varta brand.
Repeat for the other side, black wire to the negative – side of the coin cell.
And you’re done! With both sides now taped back to the wires, you can plug the battery back in to the ESL. The JST plug will only go in one way, but if you’re unsure, the red wire goes to the left when holding the tag with the plug at the top and the space for the battery at the bottom.
Now, next time this cell runs out of juice, pull out the plug again, then take of the adhesive tape from both wires and stick them back to a new coin cell, insert back into the ESL. Repeat ad infinitum! No need to buy the expensive CR2450-2P ever again.