Convert Nexus 5 To Use External DC Power

I just took apart a BL-T9 battery module from my old Nexus 5 cell phone. I had removed it as a precaution since its internal chemical situation had degraded, puffing up and pushing itself out of the phone. Even though the phone still seemed to work (or at least it would boot up) a puffed-up lithium-ion polymer battery is not a good situation.

But now I have an otherwise functional cell phone without a battery. It would be a shame to toss it in the e-waste, but it needs a power source to do more than just gathering dust. The first experiment was to see if the phone would run on USB power with the battery removed, and that was a bust. Trying to turn the phone on would show the low battery icon and then the screen goes dark again.

I then looked online for a replacement battery. (*) They range from a very poorly reviewed $10 unit on Amazon, up through the $35-$50 range. But did I want to spend that money? I don’t really need this device to be portable and battery-powered anyway. It’s more likely to go the way of my HP Stream 7 and become an always-on externally powered display, something I’ve tried earlier and plan to revisit in the future.

With my HP Stream 7 power experiments fresh on my mind, I decided to convert this device to run on external DC power as well. It won’t have a battery to buffer spikes in power draw, but that might be fine. An Android phone has lower power demand than a Windows tablet. For starters, I wouldn’t be plugging in external USB peripherals. Also with the HP experience in mind, I expect there are device drivers in its Android system image that expects to communicate with the chip in the battery module. So I’ll keep that module in the circuit and solder a JST-RCY connector where the battery cell terminals used to be. As a quick test, and one last farewell to the old puffy battery cell, I connected it to the JST-RCY connector. This electrically replicated original arrangement so I could verify everything still worked. I pushed the power button and there was no response. Oh no!

I mentally explored some possibilities: perhaps there is a thermal fuse on board the circuit board that killed the connection when it sensed the heat of my soldering iron. Or perhaps the chip would refuse to power up if the battery voltage ever sank to zero. As an experiment I plugged in USB power again, and I was presented with the battery charging animation. Pushing the power button now booted up the phone. Conclusion: if the battery had been disconnected and reconnected, a Nexus 5 requires USB power to jump start the cold boot process.

With the system verified to function (and learning the cold startup procedure with USB power) I disconnected the puffy battery for disposal. I replaced it with a MP1584EN DC voltage buck converter module (*) I adjusted to output 4.2V simulating a fully charged battery. I also added an electrolytic capacitor in the hope of buffering spikes in power draw. After using USB power for cold start, the Nexus 5 was content to run in this configuration for over a week. Perfectly happy to believe it was running on a huge battery the whole time.


(*) Disclosure: As an Amazon Associate I earn from qualifying purchases.

Nexus 5 BL-T9 Battery Teardown

Sitting in my pile of old electronics, my Nexus 5 battery’s internal chemistry has started doing something that made it puff up like a balloon. I removed the battery as soon as I noticed the symptom and thought it might be fun to take a look inside the battery module. The module might be just some packaging around a bare lithium polymer pouch, or it might be something more. It was the latter.

I peeled away the external plastic sheet and saw a small circuit board between battery terminal tabs and the phone. Looking at the phone connector, I see four electrical contacts. The two larger contacts are likely to be power and ground, two smaller pins would be consistent with data and clock for I2C or another communication protocol. However, looking closer I saw the bottom center contact is electrically connected to the large right contact, for three usable pins leaving one for communication.

This side of the circuit board also had a few bits of information silkscreened on it. BL-T9 is the name of this battery pack. UL94V-O probably refers to Underwriters Laboratories standard for device flammability. The remainder of information “NXCT 50 31” are a mystery, possibly PCB design revision numbers. The black ink printed “F9 DA” is probably a manufacturing lot number or identifier of similar purpose.

Looking at the other side of the circuit board, there are only three soldering points on the phone connector which is consistent with what we saw earlier. To its left is a silkscreened “LI176AH” and in this context it’s tempting to think it means “Lithium Ion” battery of a particular “Amp-Hour” rating, but 176 doesn’t correspond to the 2.2AH printed on the outside label so it must mean something else.

Further left on this circuit board, I see a small chip labeled “SP45AE A41711” but a search on that designation came up empty. Continuing left we see a few test points, and something I don’t recognize labeled with a “P”. It looks like a tiny circuit board with visible traces, soldered to the larger circuit board. Probing contacts accessible on either side of the “P” gave a resistance reading of 0.2Ω. My best guess is a shunt resistor for measuring electrical current flow, or possibly a fuse. (Which is also a sensor for electrical current, technically speaking.)

This was all very interesting, but retiring this battery also meant I had a phone with no battery. So I will convert it to run on external DC power.

Degraded Nexus 5 Battery Demands Immediate Removal

I’m happy I found a way to make use of the HP Stream 7 tablet, though I have no immediate use for it so I jotted down some notes before putting it away in my pile of old hardware. When I did so, I found an unpleasant surprise in that pile: my old Nexus 5 cell phone shows signs of lithium battery degradation. It has puffed up, pushing against the back panel of the phone and popping a few clips loose. This is not good. I don’t know how long it’s been in this state, but I need to pay immediate attention.

With the first few retaining clips popped loose by the puffy battery, it was relatively simple to pop the remainder loose in order to remove the back panel. However, more disassembly is necessary before the battery could be (nicely) removed.

Further disassembly meant removing six screws holding this inner shield.

Once that inner shield was removed, I could disconnect the data cable running between the top and bottom halves of the phone, and I could electrically disconnect the battery. Mechanically, the battery itself is held by adhesive strips. The puffiness pulled some loose, but the remainder required some persuasion to release. I used a bit of thin clear plastic cut from some thermoformed product packaging.

The battery has puffed up roughly triple of its original thickness. No wonder it didn’t fit inside the phone anymore.

I’m glad I was able to remove the problematic battery before it expressed its degradation in unwanted and exciting ways. (Fire? Maybe fire.) But now I have removed the battery, I might as well take a closer look.

ESA ISS Tracker on Nexus 5

When I tried a Nokia Lumia 520 to see if I could use it as ESA ISS Tracker display, I found its screen couldn’t quite manage. Displaying the entire map in a clear and legible way requires more than the 800×480 resolution of a Lumia 520’s screen. Which led to the next experiment: dust off an old Nexus 5.

Nexus 5 Android support was discontinued several releases ago, but when new it was quite a compelling device. One of the signature features was a full HD 1920×1080 resolution screen packed into just five inches of diagonal length. And given Google’s track record of mobile Chrome browser, I was confident it would be capable of rendering ESA’s HTML ISS tracker.

Unfortunately it proved to be even less suitable than the Lumia 520, due to the lack of hardware navigation buttons. This meant the Android navigation bar is always on screen, obscuring part of the map. This was similar to how a Kindle behaves, except the Kindle bar is across the bottom while the phone is over on the right.

Nexus 5 sleep timeouts

Another problem shared with the Kindle was the inability to keep the screen on. Screen inactivity sleep timeout could be set anywhere from 15 seconds to 30 minutes, but there isn’t a “Never” option like there is on Windows tablets or Windows Phone. It seems to be a persistent trend in Android devices, which is reasonable for portable personal electronics but annoying when I want to repurpose one as an around-the-clock status display. Android being Android, there’s probably a way around that limitation, but that’s not a very interesting project right now when I already have more cooperative devices at my disposal.