Just ok, not good. I got 6+hr looping a 720p video which is quite ok, but in real life usage I get several hours of screen time for browsing/reading which is fair-below average. I think v37 without the zram/throttling of v45 might have been better for battery life.

I sounds like a bug to me. You can choose which sim the data connection is using in the menus. Its set to the 3g slot by default.
http://en.miui.com/thread-50550-1-1.html

Call/chat/email support with your problem and let us know what they say.
http://www.mi.com/my/index.html

I'm certain having data connection active using the 3g sim did not stop any calls from coming through on the 3g sim or 2g sim. I don't know if the data connection was halted while the call was still active, you could try it out by making a call and then opening up a browser.

A half yes to heat and low ram issues. Not sure about fast battery drain.
The v45 rom tried to fix problem of heat and lack of ram but it didn't do it that well. The phone stutters abit and lags a little because of the zram compression trick and cpu throttling. Battery is ok if you start with a full charge.

You're looking in the wrong section. I think the non-orig section is more for posting people's experiments and the quality can be trashy.

This looks like the CM11 which is developed by jsevi/kratos in the orig section:
http://forum.xda-developers.com/redmi-1s/o...mod-11-t2909757

I haven't but I think that the cpu might be underclocked in that rom to make it possible. I think the 1.6Ghz rating might have been on the high side conditional upon good cooling which the redmi 1s does not have. Pulling back the cpu clock a little bit might be a good thing.

Maybe only if you aren't doing anything with it. The phone feels laggy because of the clock throttling and the zram compression introduced in 43.0. Simple tasks like browsing on a single tab causes the temperature to shoot up to 38C which is the limit for throttling.
And gaming causes the phone to run hot (as before) because the redmi will not throttle when a game is running.

That setting inside the default security app (which is the same or linked to the setting under battery settings) does not help with the heat issue or the laggy performance. Browsing on 1 tab will still send the temps to 38C under the (default) cpu balanced setting. I think all the performance setting does is to adjust how many apps can run in the background and the throttling limit.

Afaik the Redmi 1s is a umts phone which will not be compatible with the American AWS standard, so it will be a 2g+ phone in the states.

The Redmi 1s source code was just released less than an hour ago, so jsevi/kra1o5 can finally tweak the kernel and probably fix a few more bugs.

The TDMA rom might brick the phone. Only use WCDMA. No point installing the China rom unless you want the China apps and Chinese keyboard input as default.

The Malaysian recovery/fastboot rom is here:
http://en.miui.com/thread-84007-1-1.html

After flashing to CM11 R26 (armani group) I got 3:09hr OST for 47% battery usage (no calls during the time, on wifi). Stock miui v45 gave me slightly over 6hrs (estimate at 50%) looping 720p video. CM11 r26 is probably the most stable custom rom out there now, no need for any custom kernel. Doesn't have the lag or stutter of v45. Maybe v50 fixed some issues but I won't bother with miui anymore, its too bloated for 1gb. The miui camera will run on cm11/12.1 but does not have the option to save to sdcard.

The first reboot after a flash will rebuild the cache/dalvik/art bytecode which will suck up some battery life so that has to be taken into account. Busy themes, launchers and life wallpapers also suck up battery life and skew comparisons.

Philz or TWRP is fine. CWM shouldn't be used because its outdated on some devices and not compatible with newer versions of roms/gapps. Getting correctly built gapps package is important to avoid errors.

I didn't like the overheating and other minor issues of CM12.1 r5. And the same problems are probably across other custom 12.1 roms.