600 hours of use is a lot of hours! Keeping in mind the hours begin to subtract only when the unit is on. Which means if it would stay on for 3 and a half weeks + continuous which they will not, that is a lot of time. They fortunately have a 4 and an 8 hour timer auto shut off on them. And also if the operator would look through the screen when they turn the unit on they would see the 20% battery warning indicator which the Reticle flashes on and off five times anytime the unit is turned on and the battery is in the 20% of life. And then stays on for use after the five flashes. So if an operator has a problem with the battery suddenly going dead with out notification. It is simply an operator problem of not looking through the screen when the unit is first turned on.
Another question! Do you have the standard front sight on your rifle. If so you may want to look into a Rock River Arms Dominator Rail. It was specifically designed for the EOTech Sights for the DEA, FBI and other government agencies in the beginning. I have made previous posts explaining how to use and zeroing hints on the Dominator Rail.