Good news: after unplugging the battery and plugging it back in, the notebook seems to have charged up to 100% overnight.
To recap: if your battery is charging very slowly, try removing it briefly from the notebook and then refasten it after a few seconds. According to others on this website, this resets a small microcontroller that manages charge rate independently of the rest of the machine. In my experience, various sleep modes and improper power-off procedures may be at fault for putting this controller in a bad state.
keywords: sleep suspend hibernate battery drain slow charge power failure |