Something really strange happened a few days ago. I had kept my My MacBook Pro on charge and I knew the battery was full because the indicator light was green. I removed the charger and opened the computer, which had earlier been put in sleep mode when the battery level had come down to 5%. The moment the screen came up, I was greeted with a low battery warning.
Not only that, the battery icon was full and in red instead of black color – the battery percentage at 99% also confirmed this. This was really puzzling. To top it all, this happened a month after the one year warranty had expired!
As mentioned above, I knew the battery was fully charged – there was no question about it – and the icon confirmed it. But why did the Low Battery warning pop-up and why was the icon in red? Anyway, here are the steps I took to solve the issue.
Hope these instructions work for you too!
FYI, the images have not been altered in anyway (except cropping out the top-right section of the screen).
Update: After the incident of the Mac fully-charged battery showing up as a red icon, I noticed that the battery drained out quickly. This had me worried. However, it solved on its own after two charges; i.e., I worked on the laptop till the battery level fell to 5%, shutdown the machine and then charged it full.