Originally Posted by
cyccommute
The problem with flashlights is that not only are they more difficult to charge, you have to remove the battery to change it. If you carry spares...which you should...changing one in the dark entails disassembly of the light and fumbling with multiple small parts in the dark. A wired bike light is simply unplugged and the new battery plugged in.
This isn't really a fair comparison.
Flashlight steps :
Remove flashlight from holder
Remove back of flashlight
Shake battery out
Put new battery in
Put back back on
Put back in holder
Wired bike light steps :
Unplug light from battery pack
Remove battery pack from bike
Put new battery pack on bike
* note that the previous two steps may be non-trivial.
Plug light back into pack
Now, if you have your spare battery pack mounted somewhere so you really can just plug it in, that's fine -- but really, if you can do this, you can just have a second flashlight mounted too ready to go with even less effort and the same space taken.
This does get more complicated if your light uses multiple batteries (be it wired or flashlight) but the ones that most of us use use a single battery or single battery pack.
Personally, I don't just carry spare batteries -- I have a spare light or two. You never know what'll happen. Ideally, I've got at least two lights mounted on the bike ready to be turned on at any time.