The NiteRider Pro 12E eats up a water bottle cage. I don’t miss it because I have two cages and use a 100-oz Camelbak for my primary hydration. If I’m going for a long ride in the boonies, I’ll carry a frozen spare bottle in my panniers.
I’m a long, slow rider, so I’m not too focused on the weight of the battery. (The spare tire around my waist is much heavier than my battery light.) In my circumstances, I don’t think the battery makes much difference on my average 2.5 to 4 hour rides. The 12E’s run time at the lower power settings, 9- and 12-watts, is plenty long for those rides.
As they say, YMMV.