Flexible batteries are crucial for powering the future of flexible electronics and devices. These applications demand batteries that can bend, twist, stretch, and remain ultra-thin under diverse working conditions. Achieving this requires strategic design of battery materials, structures, and configurations that readily adapt to shape changes. Breakthroughs in key challenges, such as battery flexibility, endurance, and device compatibility, are essential to bridge the gap between battery processing techniques and the rapid, large-scale production of flexible batteries. Innovations in planar configurations, including paper-like, thin-film, origami, and spinel-inspired designs, have effectively enhanced battery flexibility. Additionally, emerging processing methods like 3D printing offer precise structure control, high material utilization, and simplified cell patterning, further promoting advancement in flexible planar batteries. One-dimensional fiber-shaped flexible batteries offer unique advantages, including miniaturization, adaptability, and weavability. These can be integrated into textiles to create wearable electronics. However, improving energy density and achieving scalable woven cells in electric textiles while maintaining safety and stability remain significant challenges. The development of truly integrated flexible electronics necessitates highly flexible batteries with both decent energy/power density and robust mechanical toughness. In such systems, intrinsic, absolute safety is paramount, as flexible batteries will face diverse mechanical stresses and unforeseen environmental conditions. This chapter provides an overview of various flexible battery designs with diverse materials and chemistries, while also highlighting crucial challenges for future practical implementation.