The voltage applied to the terminals of a storage battery for charging cannot be?

The voltage applied to the terminals of a storage battery for charging must be a direct current (DC) voltage, as storage batteries are designed to store energy in the form of chemical energy through a reversible reaction that occurs with DC.

Using ordinary alternating current (AC) would not be suitable for directly charging a battery. AC does not provide the unidirectional flow of electric charge necessary for the chemical reactions inside the battery to charge it effectively. Furthermore, charging a battery with AC could lead to damage or reduce the efficiency of the charging process, as batteries rely on a direct current to facilitate charging in the correct direction.

High voltage DC and low voltage DC can be appropriate under the right circumstances. The key is that any DC voltage applied must be within the specifications for the particular battery being charged to ensure safety and effectiveness. A constant DC charge is often preferred to maintain a steady and safe charging process.