The last multiple battery mod I bought was the Wismec
reuleaux 200W that supposedly goes to 250W with a firmware upgrade. I vape at 10W so I'm only into vapability and features and hopefully longer battery life while tootle puffing.
My
smok Koopor Plus 200W (dual 18650) bit the dust after a year or so of use. One morning it wouldn't fire. The center contact came off the spring loaded pin. I was able to squeeze the press fit contact back onto the pin with pliers, but obviously it shorted and blew the electronics when the contact popped off. It's not even a good boat anchor after that. Just a heads up about what can happen with that one.
The Alien looks promising.