Series Connection of Batteries:
When batteries are connected in series, the positive terminal of one battery is connected to the negative terminal of the next battery, and so on. In this configuration, the total voltage across the series-connected batteries is equal to the sum of the individual voltages of each battery.

- The positive terminal of the first battery is connected to the positive terminal of the second battery.
- The negative terminal of the second battery is connected to the positive terminal of the third battery.
- This connection continues until the negative terminal of the last battery is connected to the negative terminal of the previous battery.

Parallel Connection of Batteries:
When batteries are connected in parallel, the positive terminals of all the batteries are connected together, and the negative terminals are connected together. In this configuration, the total voltage across the parallel-connected batteries remains the same as the voltage of a single battery, while the total current capacity is increased.

- The positive terminals of all the batteries are connected together.
- The negative terminals of all the batteries are connected together.

Comparison of Series and Parallel Connections:
- Voltage: In a series connection, the voltage adds up, while in a parallel connection, the voltage remains the same as a single battery.
- Current Capacity: In a series connection, the current capacity remains the same as a single battery, while in a parallel connection, the current capacity adds up.
- Total Voltage: The total voltage in a series connection is the sum of the individual voltages of each battery, while in a parallel connection, the total voltage is the same as a single battery.
- Total Current Capacity: The total current capacity in a series connection remains the same as a single battery, while in a parallel connection, the total current capacity is the sum of the individual batteries.

Why Batteries are Generally Connected in Series:
- Increased Voltage: Connecting batteries in series allows us to increase the total voltage across the load. This can be beneficial when the load requires a higher voltage than a single battery can provide.
- Uniform Current: When batteries are connected in series, the current flowing through each battery is the same. This ensures that each battery is equally utilized and prevents any imbalance.
- Battery Compatibility: Series connections allow us to use batteries of different capacities or types. As long as the voltages of the batteries are the same, they can be connected in series to achieve the desired voltage for the load.

Therefore, batteries are generally connected in series when a higher voltage is required for the load.