Error 0271 set time after drained battery

I bought an X1 Carbon G6 unfortunately with a supervisor password. Since it was a good deal and nothing major seems to be locked and boot order isn't locked I decided to keep it.

I noticed when the battery is totally drained or I disconnect the battery when opening up, I get the error 2771 afterwards. I thought I was screwed but just pressing esc twice it boots normally and the clock displayed by windows is correct.

Should I be worried? It seems to work fine and I don't really want to return it. I thought the clock is powered by the CMOS battery, not the main battery. Oh and if I ever have to replace the CMOS battery, will that mean I won't be able to boot, since I can't set the bios time and date?