I find myself wondering thusly... The Sigelei 20 Watt is a nice device. It has a fixed length tube suitable for 18650s. It has an input current requirement of 10A. I have AW IMR 18490 1100mAh batteries, which have a maximum output of 16A. AW IMR 18650 2000mAh batteries would not supply enough current. AW IMR 18650 1600mAh batteries would cost another £20 and only give me 500mAh extra. The charger I keep at work won't take 18650s. So.... Can anyone see any reason why I shouldn't make a little 15mm widget to fit between the battery negative and the bottom spring to allow me to use 18490s instead of 18650s? ...or in fact, does anyone know of an 18490 tube for the 20W?