The antonyms for the word "charging up" could include terms such as discharging, draining, or depleting. To discharge is to release or unload, while to drain means to empty or remove liquid from something. Depleting refers to the gradual reduction or consumption of a resource or energy. Other related antonyms might include words like calming down, relaxing, and unplugging. These terms all suggest a decrease in energy or activity, in contrast to charging up which implies an increase or intensification of energy. Antonyms can provide helpful context and contrast for understanding a word's meaning more fully.