Some other natural ideas: Customers thanking me gives me a burst of energy. The appreciation of customers motivates me. Kind words from customers are motivating.

The grammar is is fine, but it doesn't really sound like something a native would say. There are lots of ways to express the thought. You might say: When customers thank me, it keeps me going. When customers thank me, I forget that I'm tired. When customers thank me, it makes my day.

It's better to focus on the positive. "Tiredness" is a negative. "Energy" is a positive. For this reason it sounds better to say "my energy returns".