Lithium-ion batteries are great. They have high energy density, are lightweight, and in the case of many portable devices, they can be easily swapped in and out. One problem with prismatic (the types you often find on cell phones that have a set of flat contacts on one end of the battery) packs is that they’re all custom; the cell may be standardized but the pack it’s in is often proprietary to a certain make and model. Sure, there are “universal” holders out there, but they provide poor electrical contact at best. Since I need a secure electrical connection when using my battery fuel gauges, I sought to create a more sturdy holder for the batteries I have lying around.
The construction of the holder is pretty simple. A strip of female pin header (I used a single-pin-width header but a double-width one can be used for greater mechanical strength) is used as an end-stop for the battery, and a right-angle pin header is used to create contact with the battery’s terminals and to provide the physical “clamping” needed to create a good connection. The right-angle header can be bent and soldered into place to adjust the holder to the particular cell you’re using. Additionally, be sure to use some high-quality FR4-based boards as the brown-coloured paper/resin-based boards won’t have as good resilience and strength, and probably won’t be plated through either (this improves the structural integrity of the holder since the pin headers will be under a bit of physical stress).
For connections, I have a 2-pin header (physically a 3-pin header with one removed to denote polarity) and a set of screw terminals. These are wired up using a flat ribbon “wire” used to connect solar cells together as they can handle several amps and come pre-tinned with solder.
This sort of setup can be adapted to nearly any commercially available prismatic battery, provided it uses a flat contact area on the sides.
Thanks for the tip. I’ve got a couple of used phone Li-ion batteries and was looking for a way to reliably connect them to a charger or to power up a custom device.
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I’ve been seeing these neat contacts on Adafruit and Sparkfun that they call “pogo-pins”, which are spring-loaded contacts that are often used to create a “bed-of-nails” style QC test platform for boards, or to allow for programming of a microcontroller or EEPROM that has already been soldered onto its board (maybe so they don’t have to worry about data corruption due to the assembly process?).
I would try to come up with a way to use the pogo-pins to get better contact and prevent you from having to readjust the bent headers every once in a while.
I’ve looked into pogo pins for this type of battery holder but found that they don’t provide enough pressure on the contacts for a reliable electrical connection. I haven’t had any problems with the pins getting bent (yet) as the pin headers have some amount of springiness to them.
Ahh, OK. I haven’t had a chance to get my hands on any of those pogo-pins, yet. I didn’t realize they wouldn’t make poor contact.
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