Apple MacBooks and swelling batteries. (Edited)
A found a hidden issue in my MacBook Pro (Mid 2015 model). When opening it up to clean up loads of dust inside, I've noticed that inner batteries are puffed up and their protective skins are blown with some gas. Lots of gas and lot of pressure. System information still reports plenty of charging power and no other indications of ANY battery issues. If you think that this means batteries are OK then this is far from being the case. A bit of googling produced plenty of similar cases from around the world. Where people had consumer protection laws or extended service agreements, Apple does service and replace these batteries, however otherwise you are looking at cases starting from a very expensive fix of just the battery (glued with permanent glue to the case) to a fire hazard when those batteries do explode.
Without taking your computer apart there is a way to check if you might have this issue. Turn your laptop upside down and apply a ruler on its edge across the laptop's bottom panel. Try different directions (batteries are located in the area just below your palm rest). If you see that the ruler can roll like a seesaw then there is a bow out which can only be happening due to something pushing on the panel from the inside. That something is the battery. Play safe and take this to an Apple authorised dealer for an inspection as only they might be able to provide a free fix (if you consumer protection law is applicable for you). Otherwise you can go to any computer shop who deals with Apples unofficially and get a lower price (than direct from Apple) but still expensive battery replacement. Battery alone is about £100 plus the glue issue...
Apple are still tight lipped about the situation and there is no official recall.
Here is a link to someone's story when it did explode.
https://medium.com/@dourvaris/my-2015-macbook-pro-retina-exploded-119ea5ea9d1f