Absolutely +1 for Jhawk412's advice. A CT grip is the easiest way to put an adjustable sight on a J frame so that your selected load shoots exactly where you aim the gun. And if you ever need to actually use the gun in earnest it's more likely to be in less than perfect light - where the red dot will probably be a big advantage in making accurate shots.
As for dead batteries - new CT grips come with lifetime batteries. You get a new pair every year if you call and ask for 'em. But I've found that they actually last a lot longer than a year, so I have several years' supply on hand. (Pssst - don't tell Crimson Trace.) And in my experience the batteries don't just wake up dead one day, they slowly run down and the red dot gets dimmer. So if they were working the last time you checked, they're almost certain to work for the duration of whatever gunfight you get involved in today.
As for their utility, I had occasion to use my CT equipped 638 in a BUG gun match at our club. (Shoot what you carry at multiple targets per stage, but with a 5 round maximum in each stage and no reloads on the clock - IOW, very J frame friendly.) While I had had the laser grip on the gun for several years and had practiced with it on many occasions at the range, I found that at the start of the match I reverted to my IDPA habit of lining up the iron sights before firing a shot. It was a slightly overcast day and the ranges were short, so I was aware of the red dot floating around out there, but under the pressure of the clock wasn't picking up on it as the aiming point. By the third stage, though, I was starting to focus on the red dot, and by the fifth and sixth stages I was using it exclusively. The result was that I was getting the gun on target before it was even half way up to eye level, and was taking shots as soon as the dot was where it should be. My speed was better, my accuracy was better, and most of all my confidence in the placement of each shot went way up. I could not have been more pleased with the results, but the lesson I took away is to PRACTICE UNDER PRESSURE if at all possible.
That match was shot with the 405 boot grip, and it was NOT very comfortable to shoot. I have since put a 305 grip on the gun and it is MUCH more pleasant to practice with. The 305 grip does add a bit more bulk, but the gun is always carried in a holster, not a pocket, and the slight extra bulk makes no difference in concealment in MY context. YMMV, of course.