What is component 4 in figure T-1?

The schematic symbol for a battery consists of alternating long and short parallel lines. Each pair of lines (one long, one short) represents a single electrochemical cell. The long line indicates the positive terminal, and the short, thicker line indicates the negative terminal. By stacking multiple pairs of these lines together, the symbol illustrates a multi-cell battery supplying direct current (DC) power to the circuit. This is easily distinguishable from other symbols once you recognize the alternating line pattern.