I got the GL-AR150 with the RTC working. Can I use the exact same RTC board and wire it to GPIO 1 and 17 on GL-Mifi to make it work? Is the software installation for the RTC the same? Thank you.

Yes. it should work, as basically they are the same.

Does the battery version of the GL-Mifi use the main battery for RTC? Or is it just a hard on off for the board?