It's good to have a little warning that the battery is about dead. I don't like it when some lights just suddenly go dark. It can leave you in a real pinch.
When the battery in my E1B went dead, it didn't happen while it was in use, so I didn't notice any flickering. I knew it was getting close just because of the amount of time I had used it. The next time I turned it on, it went straight to low mode. I wish I would have just left it on at that point, just to see how much additional runtime I would have gotten in the low mode after it dropped out of high. Instead, I just replaced the battery. Oh well, maybe next time!