What voltage type should never be used to charge a storage battery?

Charging a storage battery requires the use of appropriate voltage types to ensure safe and effective operation. Regular AC voltage is not suitable for charging storage batteries because batteries operate on direct current (DC) for their charging process.

When a battery is charged, the current must flow in one direction, which is characteristic of DC. Regular AC, which alternates the direction of current flow, can lead to inefficient charging, overheating, and potential damage to the battery.

In contrast, DC voltage is the most common and effective method for charging batteries, as it allows for a steady flow of electricity in a single direction, essential for the charging cycle. High frequency voltage also is not suitable as it could lead to inefficiencies and risk damaging the battery. Low frequency DC is generally acceptable for some charging applications, as it also provides a steady flow of direction-controlled current.

Thus, the best choice to identify the unsuitable voltage type for charging a storage battery is regular AC.