Operating principles of 3 common non-isolated inductive voltage converter topologies
Integrated Inductive Switch-mode Power Supply : Fundamentals on Power Stage

In battery-powered portable systems, there's no need to implement galvanically isolated voltage regulators. Starting with a battery and its time-varying voltage, an electrical consumer with a fixed supply voltage will require a voltage regulator to be inserted between its supply input and the battery to lower the voltage, or raise it [D3168] . It is even possible to implement a step-down/step-up function if the battery voltage range exceeds and then reaches a lower value than that of the consumer supply.