Cateye Rapid Mini Usb Rechargeable Rear Light (25 Lumen):

Punches above its 22g weight and designed for the minimalist, the USB rechargeable Rapid Mini offers 4 modes of eye-catching illumination.
• 3 x red SMD LEDs – 25 Lumen output
• USB Li-Ion rechargeable battery
• Mounting bracket 21.5 – 32mm
• Light mode memory
• Battery indicator
• Battery Auto Save, converts to flashing mode so you’re never left in the dark
• Recharge time: 2 hrs

Mode: Runtime
Constant: 3 hrs
Rapid: 5 hrs
Pulse: 20 hrs
Flashing: 30 hrs