[LG V40 Guides, News, & Discussion] sam_86314:
I'm not sure how many people have noticed this, but LineageOS now has an official build of LOS21 for the LG V40.

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The moment I saw the first build become available, I got to work getting it installed on mine.

For background, my V40 is a Sprint model (LM-V405UA) that I purchased new in 2019. After paying it off and getting it carrier unlocked, I unlocked the bootloader using the V35 engineering method in QFIL, and I also cross-flashed it to the US Unlocked Pie ROM. In the last month or so, I figured out how to root it and also cross-flashed it to one of the EU Android 10 ROMs (V405EBW30e). This phone has seen a botched battery replacement by yours truly, which killed the original display, so it has a used OEM replacement from eBay on it now.

The official LOS ROM is quite easy to install, though I did have to deviate from the instructions in one place. Step five of the install guide says to use dd in a rooted ADB shell to write Lineage Recovery to both boot partitions, but I couldn't get this to work. Every time I tried to do it, I got a "permission denied" error despite being rooted. I tried from the SD card and the internal storage, and neither worked.

What I ended up doing was just flashing it in QFIL. I simply loaded the image to boot_a and boot_b (after backing them up, of course). This worked perfectly, and I was able to follow the rest of the guide as normal. In theory, using QFIL instead of dd may eliminate the need to root the phone before installation, but I haven't tested that. Plus, if you're using QFIL, you might as well just root it anyway.

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Overall, the ROM runs great on the phone. It reenables the FM Radio, the telephoto camera actually works, and it looks to have support for the HiFi Quad DAC. Even the button on the left side is properly configurable now. If it had support for IMS, I'd probably go back to using the V40 as my main phone.

I have had a couple of issues, but they aren't too major. The first one is with the fingerprint scanner, but this is mostly my fault. While doing the battery replacement on this phone, I accidentally damaged the pins that connect the fingerprint scanner to the board. The stock ROM didn't care about this, and all I needed to do was apply pressure to the back of the phone for it to work. This ROM, however, gives me the "fingerprint hardware unavailable" error even if I apply pressure. I can get it to work by constantly applying pressure to the back while it boots up, and then it behaves exactly as it did in the stock ROM, but then it'll stop working again if I reboot.

For the second issue, it seems that idle battery drain is significantly greater than on the stock ROM. After 15 hours of uptime, most of which was idle, I've gone from 100% battery to 62%. I am using microG instead of GAPPs, and I do have some apps that run in the background, but this just seemed odd given how good this phone's battery life is normally. I replaced the battery back in October of 2022, so it's a relatively new battery from iFixit. I'm going to let the phone run through a battery calibration cycle to see if that changes anything.