Have you purchased the tank yet? If not I probably would advise against it for a MTL vaper. I haven't tried those coilheads but I know most of the other ones are very airy, and maybe your preference is different than mine, but I want some resistance when I'm MTL vaping. Now, for the rebuildable coilheads there is a plug that came in the TFV4 Mini full kit, not sure if you can buy seperatly but with that I was able to fashion a nice setup. Smok is coming out with a TFV4 Micro that seems to be aimed at the MTL style vaper.
Anyways just thought that was worth saying. But no at low wattages your battery life won't take a dump. The reason the TFV4 is known to drain batteries and juice stashes is because people are running at 100w+. The tank doesn't automatically drain these things, it just gives you the ability to do so.