Magneto light won't last for 20 minutes

I don't want to give such a bad review because some of the products that I buy are good. However, I bought a magneto rechargeable LED lantern from Makro Strubensvalley, and 6 months down the line it started to give problems. It only gives 20 minutes of bright light and then it starts to dim. By the end of 2 hours of load shedding it'll be gone completely. I think it was a bad product because I bought it on special. But I won't even buy anything magneto because of this terrible experience.

After paying so much money you'd think you'll get a good product, but this is just a terrible one. Others who bought their lights before mine, they're still working great, but this one I need it replaced or at least fixed.