Does IFTTT app drain battery faster in iPhone (and Apple Watch)?
I use IFTTT on my iPhone X iOS 11.4.  

When I check Settings -&gt; Battery and look at the last 7 days, IFTTT doesn't even show-up on the list of applications.  That means it's using less than 1% of my battery.  

My recommendation to you, if you're thinking of using IFTTT, is to try it with a handful of recipes for a few weeks.  Then check the battery usage and see the impact on battery life.

Now, I'm sure this will change depending on how many recipes you're using and what kind of recipes they are.  IFTTT is just woken-up by iOS at periodic intervals to check for system notifications that something happened.