Welcome @WeikangTsai, in this case I recommend cleaning the charging contacts on the back of your Fitbit Surge. With the use of your tracker the contacts can accumulate dirt, preventing from make good connection to the charger. Use a toothpick or toothbrush to clean the charging contacts and for more information try the following link: Wear and Care.
If this is not working please take a moment to reach out to our Support Team and let them know of your efforts to troubleshoot the issue and what you've already done. So they can advise you what would be the next step.
Hope this helps and keep me posted how it goes.
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