I find that even with the cache battery, I don't always pull sufficient power to keep my phone charged up, largely because I'm slow, and every time I drop below a certain speed, the phone stops registering a charge, at which point the screen comes on. Then I speed up, and start supplying a charge, at which point the screen comes on. So depending on terrain and what speed I maintain, plugging the phone in may cause it to run down faster with all the screen activity. As a result, I just charge a battery, and use that to charge my phone, so I probably would not miss the cache battery if I had to do without it.

Yeah, this is my 2nd one, too. It was already replaced under warranty once. I really like the light, and I really like the charging ability, so I'll keep it as long as possible, but if this weird, light-bleed issue is a sign of future problems, I will not be replacing it with something else. Of course if the light continues to work, I'll be happy to keep that in service for a while, but if the light fails, I'm not likely to want to keep an extra light on my bike, just so I can have a charger.

The other disadvantage of this set up is that I have occasionally had, and would like to have again, multiple bikes with generator hubs. Ideally all the bikes would have their own lights, but it'd be good if the charger were easily swapped between bikes. I wouldn't want to move my Luxos U between bikes "just in case." I'd only do it if I knew I was going to be using it on the other bike.