Battery health at 86% is actually quite poor. Once the battery reaches 80% health, it has used up its useable life. Batteries are only really good from 80-100%. Batteries are merely chemicals. Once they reach 80%, they become unstable. This is why lithium-ion batteries are rated for x amount of cycles at 80% health remaining. iPhones are 500, iPads, and Macs are 1000 cycles.
This has nothing to do with 11.3.1, but your battery is on it ways out. Take advantage of the $29 replacement before the end of the year and it will make a huge difference. Once a battery drops below 90% its noticeable that its beginning to degrade.
Also with that being said, if you have a Mac, try using Coconut battery to determine battery health. It may be worse than 86%. Apple's battery health is still in beta, and its proved not to be all that accurate thus far.