Using a step-up transformer to increase the voltage from an alternator is feasible, particularly for applications like charging multiple batteries. The voltage increase depends on the number of turns in the transformer’s copper windings. While higher voltages can reduce conductor size, they also incur higher costs for insulators and safety measures. Common voltages like 110V or 230V are suitable for domestic use, but 12V is often preferred for battery charging due to its compatibility with standard batteries and the ability to connect them in parallel. Ultimately, the choice of transformer and output voltage should align with specific requirements and market availability.