The invention concerns single and multiple cell lithium ion batteries. Embodiments of the invention concern single and multiple cell lithium ion batteries with built-in controllers that monitor the cell or cells and provide a safety disconnect when certain monitored conditions are detected by the controller. Preferred embodiment single and multiple cell lithium ion batteries have their cell or cells within a container having a positive terminal and a negative terminal. The built-in controller monitors the cell or cell for each of the following conditions: over temperature, short-circuit, overcharge, and over-discharge and the controller provides a safety disconnect when one of the monitored conditions exist. A multiple cell lithium ion battery of embodiments of the invention include a built-in controller that monitors the temperature of the cells and provides a safety disconnect that electronically disconnects all of the cells when at least one of the cells exceeds a predetermined temperature, or a controller that monitors the state of charge of each of the cells and individually controls the charge cycle of each of the cells, or a controller that monitors the temperature of the cells and to provides a safety disconnect when at least one of the cells exceeds a predetermined temperature.