Wu Zhu could be recharged through solar energy and nuclear radiation. Solar energy was his most common method of charging, and the temple was powered by solar energy, so Wu Zhu often returned to the temple to charge. In addition, Wu Zhu could also use nuclear radiation to recharge and self-repair. To be specific, when Wu Zhu was damaged, he would head to the place with the most severe radiation to repair himself. However, every time Wu Zhu returned to the temple to recharge his batteries, his memories would be erased, and he would only remember the name Ye Qingmei. This meant that Wu Zhu had developed feelings for Ye Qingmei after interacting with her, and even though he had lost his memory, he could still remember Ye Qingmei. Therefore, Wu Zhu used solar energy and nuclear radiation to recharge his batteries during the celebration. At the same time, he also displayed his emotional connection with humans. The specific charging method was not described in detail in the original book. You might need to read the original book or watch the TV series to understand.