I can only speak for my personal experience, but for what that's worth I find:
In low light/nighttime conditions the Laser dot is bright and can be seen for at least 2acres. (440'?). I know because I can shine my Crimson Trace equipped Sig P239 or my S&W J-frame 638 from my back porch into my buddy's garage with no difficulty..
It was fun the first time watching my friend and his son-in-law "ducking" when they saw the laser dot... (His son-in-law is in the Army, and in fact in Iraq now) so he picked up on the dot pretty quick..
The firearms were unloaded, obviously.
During daytime conditions at self defense range (for me 0-7') the red dot is visible and would be effective for self defense use. I find this to be true even under bright daylight conditions, and obviously overcast, or lower light just makes it easier to see.
I don't see battery life as a problem.. In the first place the little batteries last a long, long time.. I replace them yearly as I do my smoke alarm batteries and when replaced they were still bright and strong. The batteries are available anyplace, and are inexpensive.
When i bought my CT grips for my SIG P239 a promotion was in effect that gives me free batteries for life.. I'm an old fart, so that might not be as good a deal as for you spring chickens, but I'll have to say Crimson Trace is a fantastic company, and Customer Service is excellent.
I recommend Crimson Trace Lasergrips big time.. Great product, great company, great customer service... You won't be disappointed with the performance of Crimson Trace Lasergrips..
Best Wishes,
J. Pomeroy