You can run it on two or four, since it is a 2s2p configuration. Just make sure the two you insert are next to each other but turned in opposite directions in the battery holder.
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Thank´s for the advice!
I´ve doing testings running it with 2x18650 and 3x18650 batteries, but the light does not perform well with this battery configuration. It can not being run at turbo mode for longer than just a few minutes before it cuts off(not steps down). I don´t think it´s becasue of any issues with this sample, but it demands so much power so it can only be run on lower modes and for a shorter time if one does not have 4x18650 batteries inserted. Just like the manual says, running the TK75on 2x18650 is realy only for emergency situations. I am awaiting to receive a new 18650 replacement battery, and when i receive it i expect that the light will perform perfectly.