18650 Question - one works, other won't

[Firescooby]

I just got my recent order from Dealextreme. I ordered more 18650 batteries (UltraFire LC 18650 2400mAh/3.7V Li-on) I charged them and put them in my Romisen RC-T5 light and it won't work. I put the other batteries from my first order (AW +power 18650 2200mAH 3.7V) and it works. The Ultrafire battery will work in my ultrafire light that takes only one battery, but not in my lights that take two 18650's.

Anyone know what the deal is?

Thanks

 

[mdocod]

probably a simple contact issue.. the positive end of the UFs is probably slightly recessed below the level of the shrink-wrap, this makes it impossible to complete contact from cell to cell... add a small rare earth magnet to complete the circuit, but keep in mind that this increases the risk of shorting if the magnet were to shift and make contact with the inside bore of the flashlight body.