I have a collection of batteries I find cycling. Yesterday it was a Galaxy Note 4.
You don't have to cycle thousands of km to find a mangled PDA with the dislodged
battery nearby. They leave the phone on the roof to load something into the car
which requires both hands. The phone must absorb most of the 120 km/hr oblique
impact because more often than not, the dinged battery is still serviceable, at
least as a bike light.
They need to sell $0.79 clip-on LEDs on Ebay [free shipping] letting cyclists find
their own batteries. Just 2 small alligator clips, the LED, a Si rubber strap and
maybe a switch. If some kid steals your dorky looking bike light when you are
inside shopping, it's no big deal. You are only out of $0.79.