I use a MS 808 on the helmet and a MS 872 on the bar. I do not disconnect each night or on the weekend. I too don't think the glow light on the button draws enough to make a difference. One note, the batteries from MS do not come fully charged, you need to discharge them, then give them a full overnight charge to test them.
One way not to worry about the light dying 1/2 way home in the dark is to have two lights. I let each of my lights draw down to red, then run it on strobe or low until I get home or work, then charge them. They are at different charge levels, so they do not run down to red at the same time, and they can run on red for most of my 45 min commute if I put them on strobe or low anyway. I typically get around 4 days of commute morning and evening 45 min each way with the lights on strobe or low most of the time.