ok, after few days of effort the solution seems to be found :) if anyone else will stil be interested here's the story
I assume that you run in to this problem after doing rescue procedure yourself. Personally i did the fix via ssh
since the problem starts by changing original md4 partition to sda4(during rescue procedure), we need to make it be md4 again. The command that makes the trick:
mdadm --create /dev/md4 --level=1 --raid-devices=2 missing /dev/sda4
(i only guess that
mdadm --create /dev/md4 --level=1 --raid-devices=1 /dev/sda4
would do the same)
thats pretty much it, don't forget to edit the fstab back to md4 instead of sda4, reboot the drive.
some under the hood explanation :
the fuel gauge stops working since the script that controls it (residing in /usr/local/wdc/fuel-gauge ) is linked to md4 device. Editing the script by changing variable from md4 to sda4 doesn't work, yet i guess that there's a way to edit the script to make it work with sda4, but i found it easier to make it other way.
p.s. don't judge me if this method looks lame, or was mentioned somewhere before me. I was browsing this page in my spare time for about a week, or more and did not found help. Hope my post helps at least one guy happier.
feel free to ask me if it's not working for you, if i know the answerr i will try to help.
p.p.s. sorry if my english is broken :)