Lithium batteries are commonly used in mobile phones, personal digital assistants (PDA), notebooks and other computer, communication and consumer electronics (3C) products. Lithium batteries in 3C products or electric vehicles must rapidly charge and discharge. Thus, the inner temperature increases rapidly, which is a safety issue. Conversely, over charging results in unstable voltage and current. Hence, timely monitoring and safety management of data for temperature and voltage inside a lithium battery have become a popular issue. In this work, flexible micro temperature and voltage sensors were integrated in a coin cell using the micro-electro-mechanical systems (MEMS) process for in situ monitoring of temperature and voltage.