My first two endurance tests showed that my Xiaomi Yi was able to capture ~100 minutes in 1080p @25fps.
I configured the LEDs so that only the recording indicator LEDs are active (LED ring of the power button and WiFi LED are off) and WiFi was turned off.
The battery of my Yi has only past ~two charging cycles, so the battery life may slightly increase, after some more charging cycles.
If you capture in 1080p @50/60 fps the battery life will definitely decrease. I think ~60 minutes are realistic in that mode.
Battery Drain Fix!: If you notice some awful battery drain while the cam is off, your Yi might have some kind of connection between the backup battery and a metal frame inside the cam. Here is a short description how to fix it.
Bitrate / Custom Firmware
In the DashCamTalk forum there are some useful threads about the Xiaomi Yi.
For example this one, where you can find modded firmwares with higher bitrates and also a link + tutorial for creating your own custom firmware: https://forum.dashcamtalk.com/threads/xiaomi-yi-sports-camera-custom-firmware-base-1-0-7-bitrate-increased-to-30mbps-all-modes.10410/
With the stock firmware you will get 12mbps at 1080p @25fps with quality “high” (there are different data rates for the different resolution/frame rates and quality settings). My GoPro 2 will record in 14.6mbps at 1080p 25fps which seems to be good enough, although it’s not much higher than the bitrate on the Yi cam.
The 12mbps that the Yi cam uses in that mode will result in some blurry areas if there is much action going on in the scene (many details that are moving, like the footage that you will see when flying very low and fast).
The video files will be split in ~1.95 GB parts and those will be ~22 minutes long (in 1080p 25fps “high” quality).
Here is a link to a modded firmware which will allow you to get much higher bitrates. In my preferred setting (1080p 25fps) this firmware allows me to choose between 8 / 20 / 25 mbps (low / normal / high quality).
With 20mbps the files will still be split in 1.95 GB parts and they will contain footage of ~14 minutes.
Correcting the focus to infinity
Here is the link which describes how you can open your Xiaomi Yi and correct the focus, if necessary (many people report sharpness problems which are caused by a wrong focused lens).
You basically just have to remove the front of the cam (use a knife or something similar to open it) and then remove the hot glue spots around the lens. After that you can screw the lens in and out to refocus.
Problems / Bugs
The only problem that I was not able to get rid off is the file transfer via USB. My Xiaomi Yi crashes when I try to copy the files from the microSD card via USB. I tried many different cables and microSD cards, but for now the only way to get my video files is to remove the microSD card and put it in my cardreader.
Image Quality Xiaomi Yi vs. GoPro 2
You might have seen the footage that I captured with the Yi / GoPro 2 / Mobius. This time I just lined up the GoPro 2 and Xiaomi Yi footage side by side, so it’s easier to see how they compare.
In my opinion the Yi does a great job (good white balance, details and sharpness), especially for the attractive price.