In the thread about buying new Gill batteries, I mentioned that I had just put in a battery tender, which is supposed to increase the life (hat tip to Adam, who gave me the idea). I also put in two new batteries at that time, about 18 months ago.
Before that, I was replacing them about every 18 months - 2 years.
So, 18 months in, at the 150 hour the batteries passed with 100%. Usually at this point they tell me they barely passed or just failed and I end up replacing them, either now or in 6 months. So to have them at 100% is really impressive.
So I think the battery tender is working out well.