I own a Lemfo LEM10 and it works really well. The main issue I have is whenever I activate the Bluetooth connection, the battery is draining really fast, even if there is nothing connected to it.
So I did my research and I finally found the solution to that problem. You will need to install the application « Bluetooth Visibility Fix » from the Play store. It is free and works nicely.
From the app, you then have access to a more detailed Bluetooth settings. By default, we only have access to On or Off but there is more.
It seems that when Bluetooth is on, the watch (at least my LEM10), is in discovery mode by default, meaning it is scanning for all Bluetooth devices and is also discoverable. This is draining a lot on the battery.
With the app, you can set the mode to only known devices or even to only connected devices. This is reducing drastically the battery usage when idle. The app also lets you have more control on the Bluetooth connection when disconnecting from a device.
Anyway, the simple fact to set the mode to « Only for paired devices » is preventing the watch from scanning the whole neighborhood for nothing.
I was able to last the whole day with Cellular ON, Bluetooth ON, GPS On, Steps tracking on…
Using the Bluetooth for audio still drains more battery when in usage but at least, when it is not connected, the battery drain seems to be negligible,
Let me know if it did help you with your device in the comments.
Have a great day!