So I had been wanting a new powerful LED flashlight for a toy and I came upon the TK21. I thought what a great compromise of size and output. I ordered one with four new tenergy 18650's and waited impatiently for about 5 days. I finally got it in the mail and tested it out that night only to find out that the turbo mode only stays there for about five to ten seconds and steps down to high. I am devistated by this problem because I was excited to have a new flashlight. I sent it back for a different one and hope that when I get the new one it will be normal. I hope this isn't a manufacturing defect. Anyone else out there experiencing problems with their's? By the way the light itself was awesome, my brightest one by far! I cannot wait for the replacement to come.