My apologies to VelvetElvis and Mrs_Often, but I keep forgetting to write up my findings with the boks they supplied.
The short answer is that they had no noticeable effect on the battery life of my Glo.
The very incomplete log for the week before last is:
20130211 09:20 75% Opened book from VelvetElvis - p207
20130211 13:39 75% Checked - turned to p213
20130211 15:24 71% Checked - turned to p221
20130213 00:17 64% Opened book from VelvetElvis - p221
20130213 10:48 64% Checked - turned to p232
20130213 15:38 64% Checked - turned to p243
20130213 16:25 64% Paged through library looking for book
20130213 16:26 62% Started reading 30 page story
20130213 18:08 62% After reading continuosly on train. 30pages + find another story and 25 pages of 30 page short story.
20130214 00:16 61% After sleeping with no selected book. Then finished short story
20130214 00:30 59% Opened Baldacci book, turned to page 18
20130214 09:01 59% Checked - turned to p28
20130214 18:28 59% Checked. Searched for book to read. Read for 1 hour 20 minutes
20130215 01:07 52% Read for 10 minutes. Opened Baldacci.
20130215 09:02 52% Checked - turned to p28
20130215 15:38 51% Checked. Looked at book list
20130216 00:06 47% Checked. Finished last three pages of book. Looked through book list.
20130216 09:15 47% Read 10 pages
I haven't account for all the time. But, at no time on sleep did the battery level drop more than 2%. I think I read more than I usually do in that time. I have my daily commute home and read about 1:20 then. Plus whatever at home. There was a four hour session on the 11th or the 12th, and two hours on another. That means I read at least 15 hours during that time. And for at least a quarter of this, the light was on.
About the only thing is the length of time for the sleeping. The longest was about 10 hours. There might be something happening with longer times. Maybe the device wakes and does something after 12 or 24 hours.
It doesn't help the people that are having battery life issues, but, I am happy with this. It looks like two weeks without a charge would be easy and maybe even a month. But, I don't think that would happen as the only reason I woudn't connect and charge is if I was reading a lot more than usual. And that is running the battery down.