Why did my smart only charge to about 90 %?

  • No need to worry, that's normal. At long intervals, or better said in rare cases, it does that.

    The background is simple: The BMS was unsure and therefore decided not to fully charge the battery. This is a pure protection mechanism. Next time it will charge to 100% as usual. As already writen here (Battery conservation), you do not have to pay attention to the battery, it doese that already for you.