To have a good power management especially for portable devices it is necessary to use the whole battery voltage range (e.g. of Lithium-ion batteries), to provide a fixed output voltage of for example 3V. In this paper a fast transient (FT) current mode buck-boost DC-DC converter with adaptive pulse skipping (APS) and adaptive compensation capacitance (ACC) is proposed. The buck-boost DC-DC converter can work in three different modes, buck, boost and buck-boost. It cannot only use the whole battery range from 2.7V to 4.2V, but also has a good response time with a low voltage undershoot/overshoot at load current variations, due to the APS and the ACC. With the proposed fast transient techniques, improvements could be made in the voltage overshoot/undershoot and the response time. In boost mode, the improvements, in the voltage undershoot and the response time from light-to-heavy load (100mA to 500mA), are 16.7% and 58.8%, respectively. In buck mode, 40% and 49.2% and in buck-boost mode, it is 10% and 63.9%. In case of a load variation from heavy-to-light load (500mA to 100mA), similar results could be reached in every operation mode. The proposed DC-DC buck-boost converter realizes a good power management and a good transient performance to generate a stable supply voltage for portable devices. Its working frequency is 1MHz.