In this study, rechargeable thin solid-state lithium batteries on polyimide substrate were developed and characterized. Excellent performances were noted in terms of cycle life (0.05% per cycle at high current discharge) and flexibility (up to 300 cycles at harsh bending radius 0.65 cm). In addition, multiple flexible cells can be readily connected in series or parallel arrangements to match a wide variety of application requirements using different foil-to-foil integration techniques. The interconnections were fully validated by the realization of a flexible energy autonomous system based on flexible lithium thin batteries for indoor air quality sensing with radio frequency communication capabilities. The excellent mechanical flexibility and stability of capacity values of these lithium-based thin film batteries make them particularly suitable for system-in-foil applications.