Diagnosis

Just picked up few Jetbeam III-M R5's. One of the batch will run for about 1min then flicker for a few moments and not turn on again for 10min after which then I only get 5-10 seconds of run time before it shuts off again. Leave it for an hour and it's good for another minute or so. Checked all the basics....contacts ect. Not sure what the issue is.... overheating?

Anyway could do with some tips or suggestions. The dealer is local but would still rather solve it myself then bother to return.