thanks so much with the help with this everyone. Most appreciated.
About using flat tops in the device, no I don't think you "have" to use them. I have read of some people having problems with not being able to close the door with button tops though so apparently some with button tops are too long. One person used 18650 AW button tops in that device & said his did not fit. So I wanted to make sure to get flat top to avoid that problem.