Battery draining extremely fast

I bought the laptop like 2 months ago and until now I've been using it exclusively plugged in.

I turned on conservation mode the whole time.

Today I unplugged it and took it with me, when I unplugged it was at about 75%. Hours later I open it and it is at 19% and then it begins to drain at like 1% per 30 seconds. Literally nothing was running, power saver was on, it just began to drain extremely fast until I turned it off.