Connecting two or more batteries together into a single battery system, known as a battery bank, allows you to increase capacity and voltage to power larger devices. But there are important electrical and safety considerations, especially when handling lithium battery packs.
In this comprehensive guide, as a professional lithium battery pack manufacturer, I’ll explain step-by-step how to properly connect two battery packs in series or parallel to create a safe, higher-performance battery bank for your application.
Why Would You Connect Battery Packs?
You may want to connect separate battery packs for a few key reasons:
- Increase capacity – Connect packs in parallel to combine capacity and amp-hours. This extends runtime for power-hungry devices.
- Increase voltage – Connect packs in series to step up system voltage. This allows compatibility with devices needing higher input voltage.
- Flexibility – Using multiple smaller packs instead of one huge battery allows flexible mounting, transportation, and charging.
- Redundancy – Separate packs provide redundancy. If one pack fails, the system can keep working off the other one.
Key Considerations When Connecting Packs
Before connecting battery packs, keep these guidelines in mind:
- Use lithium packs with compatible chemistry – For example, always connect Li-ion to Li-ion, never to LiFePO4.
- Match packs by voltage – Identical system voltage avoids imbalance.
- Ensure both BMS systems are compatible – Avoid conflicts between battery management systems.
- Check pack state-of-charge – Significant charge differences stress packs when first paralleled.
- Add protective devices like fuses – Help prevent damage from overcurrent.
- Battery expansion – Account for swelling batteries in mechanical design.
- Check certification like UL listing – Improves safety compliance.
Now let’s get into specifics on how to connect packs properly in series and parallel.
How to Put 2 Battery Packs Together?
Connecting Batteries in Series
Connecting packs in series increases total system voltage while capacity stays the same.
To connect in series:
- Orient packs so the negative terminal of the first pack connects to the positive terminal of the second pack.
- Confirm both packs are of equal voltage and capacity.
- Affix interconnected packs securely using insulating mounts to prevent short circuits.
For example, connecting two 12V 10Ah Li-ion packs in series produces a 24V 10Ah system. Total energy remains equal to a single pack, while voltage doubles to 24V.
This higher input capability allows using battery banks with 24V equipment like mobility scooters or electric bikes needing the higher voltage.
Connecting Batteries in Parallel
Alternatively, connecting packs in parallel sums total capacities while maintaining the same system voltage as an individual pack.
To connect parallel:
- Connect the positive terminals of both packs together.
- Connect the negative terminals of both packs together.
- Ensure protective measures like fuses to limit current.
For example, two 12V 10Ah Li-ion packs connected in parallel produce a 12V 20Ah battery bank, doubling total energy storage while keeping supply voltage equal to an individual pack.
This extends run time for electronics like drones, perfect for long flights needing the extra capacity.
Safety Tips When Connecting Battery Packs
- Never short circuit terminals – Always keep insulation in place.
- No loose wire strands – Trim wires and ensure solid contact with terminals.
- Avoid directly touching cells – Sparks, heat, or nail penetration can trigger failures.
- Add protective devices – Fuses, current limiters, BMS imbalance detection.
- Secure packs mechanically – Prevent damage from vibration.
- Check state of charge – Before connecting packs in parallel, drain or charge weaker pack to match voltage.
- Monitor temperatures – Heat buildup accelerates aging and risks thermal runaway.
In Closing
Connecting together well-matched lithium battery packs in series or parallel allows increasing capacity or voltage compared to using just a single pack. Pay special attention to safety. Following best practices during mechanical and electrical integration keeps your custom battery banks running optimally. Reach out if you have any other battery bank questions!
