Which of the following statements is generally true regarding charging several aircraft batteries together? 1. Batteries of different voltages (but similar capacities) can be connected in series with each other across the charger, and charged using the constant current method. 2. Batteries of different ampere-hour capacity and same voltage can be connected in parallel with each other across the charger, and charged using the constant voltage method. 3. Batteries of the same voltage and same ampere-hour capacity must be connected in series with each other across the charger, and charged using the constant current method.

• A. 3
• B. 1 and 2
• C. 2 and 3
• D. 1 and 3

Answer: (B)

When charging several aircraft batteries together, how you connect them changes how voltage and current divide among them. In a series connection, the same current flows through every battery, so a constant-current charging approach is used for the string. If the batteries have different voltages but similar capacities, the current stays the same through all of them and the individual battery voltages rise as they charge, so charging the string with a controlled current is generally workable as long as you monitor the pack and its total voltage to prevent overcharge.

In a parallel connection, all batteries share the same voltage, so a constant-voltage charging method is typical. The charger sets a single voltage across the group, and each battery draws current according to its own internal resistance and state of charge. Batteries with the same voltage but different ampere-hour ratings can be paralleled; the larger capacity simply draws or accepts current in proportion to its characteristics, while the other cells balance as allowed by the setup.

The idea that batteries with the same voltage and same capacity must be connected in series and charged with constant current isn’t generally a requirement. You can often parallel them, or charge them individually, depending on the configuration and equipment. So the valid statements are that series charging with constant current and parallel charging with constant voltage are typical approaches, while the notion of a mandatory series arrangement for identical a-h ratings isn’t generally correct.