Cause of the Issue

The cause of the repeated reboots in this case was a malfunctioning power switch. This issue is not visible from the outside, making it difficult to identify.

Symptoms

The final symptoms were as follows:

• The Nexus 5 repeatedly restarted at intervals of about 2 seconds. When it booted up, the Google logo appeared briefly, then the power went off, and it restarted.
• Sometimes, if you continuously pressed the power button during startup, it would occasionally boot up.
• Even when it did start up, it exhibited behavior like a long press of the power button (showing the “Power off” menu).

Pressing the power button rapidly during startup seemed to interrupt the long-press detection of the power button, allowing it to boot up.

When the Issue First Occurred

It happened when I was heading out for dinner. I was checking my emails on the train, and when I got off at the nearest station and tried to use my Nexus 5 to check the map, something seemed different. It looked like the OS had been updated somehow, even though I had disabled OS updates. It had seemingly updated to Android 6 without my knowledge. As I was trying to find the map, the device suddenly powered off.

It kept restarting, and before it could fully boot up, it started showing “Preparing apps” or something similar, indicating that a lot of processes were running. It was a frustrating situation since I was running late for dinner, and I had no way to contact anyone since all my contacts were in the phone. So, I went back to the station, found a public phone, inserted 100 yen, and called my workplace. However, I received a message saying that the office hours had ended, and my 100 yen was gone. It was truly a frustrating situation.

Relying on my memory, I decided to walk to the dinner location. I knew it was nearby, but I had no information about the restaurant or its name because everything was in my Nexus 5, which was now essentially useless.

Suspected Battery Issue

Some people with similar issues on their Nexus 5 reported that replacing the battery solved the problem. However, in my case, replacing the battery did not resolve the issue.

My Nexus 5 was about 3 years old, and its battery never lasted just 1 hour, so the possibility of a battery issue seemed very low.

I did try replacing the battery, and the same symptoms persisted. The battery I used was the Google Nexus5 PSE Certified Replacement Battery (Nexus5).

This battery worked fine, so I recommend it for those who want to replace their battery.

Suspected Android 6 Issue

There were suspicions that Android 6 might be the culprit, but in my case, it probably had no impact. While it did update to Android 6 at some point, it was working fine after removing the power switch.

Why I Removed the Power Switch

I initially tried to remove the power switch using a soldering iron, thinking it was the cause on the motherboard. However, even after applying heat, the solder didn’t melt, making it impossible to remove. So, I had to resort to a 力(ちから) (forceful) method.

I have detailed the specific rescue method in How to Recover from Nexus 5 Endless Reboot Loop and Retrieve Data.

The Nexus 5 I used was manufactured by LG. I’ve used smartphones from Japanese manufacturers for over 2 years without encountering such problems.