Should Lead-acid Batteries Be Connected in Series or in Parallel to Increase Battery Life?

The longevity and performance of lead-acid batteries in a system are influenced by how they are connected—whether in series or in parallel. Here are considerations for each configuration with respect to increasing battery life:

Series Connection

Advantages:

1. Consistent Current: All batteries receive the same charging and discharging current, which can promote uniform aging if the batteries are well-matched.
2. Simpler Monitoring for Voltage: Easier to monitor the overall voltage of the string compared to multiple parallel strings.

Disadvantages:

1. Imbalance Risks: Differences in capacity and state of charge (SoC) can lead to imbalances. One weak or faulty battery can affect the entire string, potentially reducing overall lifespan.
2. Overcharging/Undercharging: Without proper balancing, some batteries may be overcharged or undercharged, leading to sulfation or other degradation.

Parallel Connection

Advantages:

1. Voltage Consistency: All batteries are maintained at the same voltage, reducing the risk of individual batteries being overcharged or undercharged.
2. Easier Maintenance: Faulty batteries can be identified and replaced without affecting the whole system.
3. Load Sharing: Current is shared among all batteries, which can reduce the strain on individual batteries.

Disadvantages:

1. Current Imbalance: Differences in internal resistance can lead to uneven current distribution. Batteries with lower resistance will take more load, potentially leading to uneven aging.
2. Complex Wiring: Requires more connections and careful wiring to ensure balanced current distribution.

Recommendations for Increasing Battery Life

1. Battery Matching: Use batteries of the same type, capacity, and age. Mismatched batteries can cause imbalances in both series and parallel configurations.
2. Regular Maintenance: Perform regular maintenance, such as checking electrolyte levels, cleaning terminals, and ensuring proper charge cycles.
3. Balanced Charging: Whether in series or parallel, using a battery management system (BMS) or balance chargers can help ensure each battery is charged and discharged evenly.
4. Avoid Deep Discharges: Lead-acid batteries have a longer lifespan if they are not regularly deeply discharged. Keeping the discharge depth to around 50% or less can significantly increase longevity.
5. Temperature Control: Maintain an optimal temperature range for the batteries, as extreme temperatures can accelerate degradation.

Application-Specific Considerations

• Series Configuration: Often used in applications where higher voltage is required, such as inverters for solar power systems. Good for systems where uniform charging current is beneficial.
• Parallel Configuration: Ideal for applications where flexibility, ease of maintenance, and scalability are important, such as in RVs or marine applications.