♫Do You Want to Build a Battery Pack?♫ (For My Heated Pants)

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Here’s the humble two cell battery pack which came with my heated pants. Woefully inadequate it would turn out, and not only because of the paltry number of cells. To see what’s what, and exactly what all can be done to fix the abysmally low run time of this pack, we’ll have to crack that sumbitch open:

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There’s the first problem. Generic cells, probably no more than 2200mah. I don’t even have to go to the absolute top end of 18650s available today in order to do much better than 2200mah. But these particular cells aren’t the focus of this article.

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Really, I only need that little PCB (printed circuit board) which contains all the electronics for handling charging, cell management/protection and so on. With that little fucker snipped out, I can begin to build a bigger, better battery pack around it.

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Here’s the other ingredients: Two battery boxes that hold 2 cells each, in series (the two boxes will themselves be wired in parallel, as the pants require 7.4 volts) and the cells, in the little white boxes. I chose Panasonic NCR18650s for this.

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They aren’t the absolute best, but they’re very close, and if you go one step down from the best you will enjoy a steep drop in price while still getting 99% of the benefit. The absolute best right now is the Sanyo NCR18650-GA, but the price difference per cell between those ones and these was non-trivial.

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Here the battery boxes are, super glued back to back. I use cyanoacrylate glue with an accelerant spray so it cures in a few seconds. The wire endings are twisted up appropriately for parallelization of the two 7.4 volt cell pairs.

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Now for a bit of soldering, which I did in a different room for better air circulation. I am not yet totally sure if it works. The charger light comes on when it’s plugged in to charge, but the pants button only lights up for a split second when pressed (with this battery pack connected.)

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So, there’s still some troubleshooting to be done. This happened the last time I replaced the cells in my old heated gloves, so it’s NBD and totally resolvable, just needs some further tampering. I’ll pick up some shrink wrap from Harbor Freight tomorrow to surround it with, to keep those wires under control and to protect any exposed solder points.

Once I’ve perfected this one I’ll build another identical to it. That way I can have one on the charger while the other is being used. Even just replacing the no name Chinese 18650s would yield a significant boost to run time, so doubling up the number of cells on top of that ought to be overkill, which is always the result I aim for. More to come.

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