I hate

USB chargeable lights.

• They last a tiny fraction of the time battery powered LED lights did. I used to get whole seasons, months, out of my old Knog Frog. The new improved USB equivalent manages two or three days.
  
• They give fuck all warning before they go OUT leaving you totally lightless (you'd get days, even weeks of diminishing wattage to remind you with batteries)
  
• When they go out you can't just pull over and buy batteries
  
• You have to take them off the bike to charge them. Or forget to charge them. Or charge them then forget to put them back on the bike
  
  

Grrrr