I've had my Holosun 507K X2 for about 3 years now. I'm on my 3rd battery.
When my 1st battery died, there was no warning. The dot was working when I did my daily function check and 2 hours later when I was about to leave the house again, I did another check and it was off. Luckily, I have spare batteries. This was on the way to take my HI CCW shooting test.
Now this 2nd battery was dying. The red dot was blinking slowly. Like it would flash off every 5 seconds for 1 second and then come back on. And I wasn't able to change the brightness of the dot either. So I think this is the low battery indicator, which I didn't notice the last time. A camera type low battery icon would be helpful, but I get why they can't do it. The projection of the red dot would have to add another type of image, which takes up space.
Meanwhile, Mrs. CMO's red dot is still on it's first battery and it's been over 2 years and closer to 3 years.