The downside is those rechargeable batteries are low current types... often under 1000ma. so they won't last long in a device like a portable CD player or flashlight. A single LED is different tho. I've picked up discarded solar landscape lights that folks toss out. I scab them for the solar cells. Often the PCB boards are corroded beyond any parts salvage. Enough of them wired together make for a small charger to a 12v deep cycle battery I have connected to a 120vac inverter.