Weird things about battery percentages

[hotdogPi]

Today, I was playing a game on my iPhone (Toy Blast, to be specific). My battery was going down from the 60s as normal. After I stopped playing, I entered the Harvard Museum of Natural History when it opened at 9:00 AM. My phone was at 28% the entire time from 9 AM to 2:30 PM when I plugged it in at home, not going down for anything. I wasn't using it much, but I did play the game for at least 10 minutes, as well as taking photos.

My old laptop would often go down 3%, then up 2%, then down 2%, etc., always staying within 3% of the actual number. It would not do this when charging or when Minecraft is open (Minecraft uses up battery extremely quickly). My current laptop doesn't jump up and down randomly, but Minecraft is still extremely demanding, and my battery will often go up after closing it. It also once turned black at 11% when Minecraft was open.

My 2010-2016 laptop once had the fan stop working because something was stuck in it. This caused the cursor to jump around after about 15 minutes of use, making it almost unusable. However, it did double the battery life. Putting it on a room fan would fix the cursor jumping issue. What I don't understand is that doing this also made the battery time go back to what it usually has – the computer isn't using its own fans, so why does battery life decrease?

All my laptops are MacBook Pros.