Hi. Having the exact same problem right now with my laptop's sister. I was very disappointed because we got the i7 version for her. But my assumption is since the 330S has "fast charging" enabled, the laptop probably prioritizes that instead of performance even when plugged in. as you said, it starts working fine when plugged in as long as the battery is at 100%.
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To follow up, please let me know if anyone finds out how to disable the fast charge function. We bought this laptop for her for her light video editing and photoshop hobbies. Having this problem will render this laptop useless since such programs will definitely draw a lot of performance power thus draining the battery quicker.
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Thanks!