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Macbook Pro battery draining overnight
(i.imgur.com)
I've got a 2.9 GHz 6-Core Intel Core i9 Macbook Pro (yes, the one with the touchbar and the keyboard nobody likes)...
Anyway, it's been working great, aside from this issue which seems to happen on occasion, when I don't keep it plugged in overnight. It will just drain real fast sometimes.
What causes batteries to just drain over the course of an hour or so?
Could be a task is still running in the background that prevents your Macbook from going to sleep. You can find it in the activity monitor and force-close it.
But also, as others have noted already, your battery needs service.