I've never tested it and it hasn't been a noticeable issue, but I'm used to changing out batteries pretty frequently on thermals. I think manufacture states around 5 or 600 hours.
I change the batteries out yearly.
While I know that the battery is still fine, I put a new one in the sight and keep the older one for use in one of my flashlights.
Overkill likely but I know my sight will be functioning.
Have one on a 458 socom and never an issue. Don’t remember the exact model number but it’s the Brownells T Dot version. Battery life is decent, not sure of an actual number of hours