Got a bad draw and ended up a bad 18650 Ultrafire 4000mAh battery. Fully charged, it gets 3.7V, but it wavers when you physically shake the battery. It goes to 3.5 and then 3 and then 2.8V. You shake it and it could give you anything in between. The other identical one of the pair I bought is fine. However, I feel something in both these 4000mAh moving when I shake it compared to the completely solid red Ultrafires 3000mAh I have.
The broken one results in a really dim light. So dim that staring at the lit flashlight LED doesn't hurt your eyes. Modes don't work.
I got a refund on both already.
So anyway to fix it? If I chuck it, is trash fine?