I've had the Crimson Trace grips on my carry pistol for three years or so;

and I finally had to put new batteries in.  Not bad.

Especially considering I've left it on except when doing sights-only practice; that's a LOT of on & off, both shooting and demonstrating them to people.

Added: It uses two CR2032 batteries, which are rated as 3v.  I checked the old with a volt/ohm meter, and they still show 3; but they sure weren't putting that out to the laser.