Ultratac K18

Is this the button top of the cell you posted above.

http://www.allbatteries.co.uk/lithium-rech-industrial-battery-imr-10440-v1-aaa-li-mn-3-7v-350mah-pp-acl9021.html

John.

I own the SS K18 paired with Efest 10440 flat top. Flat top works fine.

+1 me to!

It is not your traditional FT. It protrudes a bit allowing it to make contact.