BP-4L Battery Charger
Nov 10, 2017
4 minutes read

While you're reading this, keep in mind that I'm available for hire stupid!

My phone recently met with a terrible fate, hurtling to the ground at speed, putting an abrupt end to a particularly stressful phone call on a particularly stressful day in the middle of a particularly stressful week. This meant that I was without a phone for a while. I was mostly okay with not having a phone - the only thing I really missed was having a magical disembodied phantom ask far-off machines where I should go based on where even further-off machines said I was and my own personal whimsy about where I wanted to be. That is, I missed having maps. I got used to looking up directions before leaving my house though, and that was that problem solved.

My fiancee had given me an iPod Nano a while back, which had sat on my desk doing not a lot of anything. It’s now been promoted to “Chief Portable Electronic Device” and “VP of Music,” with my Gameboy Color backing it up as “First in Command of Entertainment” when I have to take a train somewhere.

Unfortunately it turns out it’s pretty difficult for everyone else to not be able to contact me for big chunks of the day, so I dug out my trusty Nokia E71. I’ve had this phone for about eight years now, having received it in a trade for a couple of Pentium 4 Prescott chips and accompanying motherboards. Decent trade in hindsight. It still keeps charge for a couple of days, works on 3G, has a camera, and supports a very rudimentary web browser. Given that most of the “smart” functionality it came with is tied to the services of a now-defunct Nokia, it’s about as non-distracting as phones get. I’ve come to appreciate this.

At some point, moving between houses, shifting electronics around, recycling various bits and pieces, I managed to lose the charger for this phone. This meant I would have to improvise. It just so happened that I’d ordered some LiPo chargers in late 2016 for some unrelated electronics projects, and they worked perfectly for charging the battery via USB. This was pretty close to perfect! I didn’t have to get another adapter, I didn’t have to order anything, and I’m pretty sure these purpose-built charging circuits would be kinder to the battery than even the one inside the phone. Only problem was that the battery has little slots for tabs to go in, and the charging circuit has solder pads to connect wires to.

For a few weeks I was fiddling around with wires every time I wanted to charge my phone’s battery, bending them just so that they wouldn’t fall out and their own spring tension kept them in place. At least until I moved my left arm and bumped them out of the way, resulting in another couple of minutes getting them in just the right position again. As an exceptionally lazy person, this simply would not do.

Enter my new battery charger, and the point of this post! Enough of the story, it’s time for pictures.

My battery charger in its first iteration

If you look closely, you’ll see there are two pins sticking into the slots for the battery. This worked, but was a little clumsy. I could do better.

My battery charger with its cage, picture shot from the side

By attaching some stiff wires to the PCB, I constructed a small cage to both guide the battery into the correct position, and hold it in place while it charged.

My battery charger with its cage, picture shot from above

The status LED from the charging circuit is still visible, even through the board.

My battery charger with the battery half-inserted

Here you can see the battery sliding into position.

My battery charger with the battery fully inserted

This is what it looks like in operation, actively charging. The status LED is red while charging and blue when complete.

Just listen to that satisfying click. Perfect.

I hope this post serves as inspiration for everyone reading to go hack up your own little piece of gear if you want it. When you make things yourself, you get to have them exactly how you want them.

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