If you wonder why your Polar mod clock loses time so much, it’s because the clock stops when you remove the batteries and resumes when you insert the batteries. I noticed how the time lagged when I swapped batteries and so I removed them for a few more minutes and noticed the clock lagged a few more minutes. I guess it has a software clock and not a hardware clock.
I tested my VBoy 200W the same way and no time loss, so it must have a hardware clock. I never expected a software clock.