Series vs Parallel Marine Lithium Batteries
Learn how series and parallel battery connections affect voltage, amp-hours, kWh, BMS limits and current sharing.
Parallel
Two 12.8V 200Ah batteries in parallel:
- voltage: 12.8V
- capacity: 400Ah
- energy: 5.12kWh
Series
Two 12.8V 200Ah batteries in series:
- voltage: 25.6V
- capacity: 200Ah
- energy: 5.12kWh
Do not assume every battery supports every arrangement
Check manufacturer limits for maximum batteries in parallel, maximum batteries in series, whether series-parallel is permitted, BMS communication, balancing requirements, current sharing, age matching and firmware.
Parallel current sharing
Multiple parallel batteries should be connected so each battery sees similar path resistance.
Poor layouts can cause one battery to work harder than another.
Make the installation verifiable
A credible marine installation should be inspectable, documented and recoverable after a protection event. The battery label alone cannot show whether fault current, isolation, charging control, mounting and essential services have been addressed.
- Document cable sizes, protection ratings, isolation points, charging settings and BMS warning or shutdown logic.
- Confirm that terminals are protected, equipment is restrained and the location is suitable for heat, water and service access.
- Have the completed system commissioned and retain the drawings, settings, test results and equipment manuals aboard.