How to Wire a 48V Battery Bank: Series, Parallel, and Series-Parallel
A correctly wired 48V battery bank is essential for safe, efficient off-grid operation. Wiring mistakes can cause unbalanced charging, overheating, or even fires. This guide covers the three main configurations and best practices.
Understanding Series vs Parallel
Series Connection
Connecting batteries in series adds their voltages while capacity (Ah) remains the same. Four 12V 200Ah batteries in series = 48V 200Ah (9.6 kWh).
Parallel Connection
Connecting batteries in parallel adds their capacity while voltage remains the same. Two 48V 100Ah battery packs in parallel = 48V 200Ah (9.6 kWh).
Series-Parallel
Combines both methods. First create 48V strings (series), then connect strings in parallel for more capacity. Example: Two strings of four 12V 200Ah batteries = 48V 400Ah (19.2 kWh).
Configuration 1: Four 12V Batteries in Series (48V)
The simplest 48V configuration:
- Connect Battery 1 positive to the positive output cable (to inverter)
- Connect Battery 1 negative to Battery 2 positive
- Connect Battery 2 negative to Battery 3 positive
- Connect Battery 3 negative to Battery 4 positive
- Connect Battery 4 negative to the negative output cable (to inverter)
Result: 48V at the capacity of a single battery (e.g., 200Ah = 9.6 kWh)
Configuration 2: Two 48V Packs in Parallel
For Felicity LiFePO4 48V battery packs:
- Connect Pack 1 positive to the positive bus bar
- Connect Pack 2 positive to the same positive bus bar
- Connect Pack 1 negative to the negative bus bar
- Connect Pack 2 negative to the same negative bus bar
- Connect bus bars to inverter with main cables
Result: 48V at combined capacity (e.g., 2x 100Ah = 200Ah = 9.6 kWh)
Configuration 3: Series-Parallel (Largest Banks)
For banks exceeding single-string capacity:
- Create String A: four 12V 200Ah batteries in series = 48V 200Ah
- Create String B: four 12V 200Ah batteries in series = 48V 200Ah
- Connect String A positive to String B positive (bus bar)
- Connect String A negative to String B negative (bus bar)
Result: 48V 400Ah (19.2 kWh)
Cable Sizing Guide
| Maximum Current | Minimum Cable Size | Maximum Length (one way) |
|---|---|---|
| 50A | 10mm2 | 3m |
| 80A | 16mm2 | 3m |
| 100A | 25mm2 | 3m |
| 150A | 35mm2 | 3m |
| 200A | 50mm2 | 3m |
Critical Safety Rules
- Use identical batteries: Same brand, model, capacity, and age in every string
- Equal cable lengths: All interconnect cables must be the same length to ensure balanced current flow
- Fuse each parallel string: Install a DC fuse on the positive cable of each parallel string
- Torque connections: Use a torque wrench on all terminals — hand-tight is not enough for high-current connections
- Never mix chemistries: Do not combine LiFePO4 with lead-acid in any configuration
- Check polarity twice: A reverse polarity connection can cause explosion or fire
Testing After Wiring
- Measure total bank voltage with a multimeter — should be approximately 48V (52-54V when fully charged)
- Measure each battery or string individually to verify balance
- Check all connections for heat after 30 minutes under load — warm is OK, hot means a loose connection
Frequently Asked Questions
How many 12V batteries do I need for a 48V system?
You need a minimum of four 12V batteries connected in series to create a 48V bank. For more capacity, add additional strings of four batteries in parallel. Always use identical batteries throughout.
Can I mix old and new batteries in a 48V bank?
No. Mixing batteries of different ages causes imbalanced charging and discharging. The older batteries will weaken the newer ones and may fail prematurely. Always replace all batteries in a string at the same time.
What happens if one battery in a series string fails?
If one battery fails in a series string, the entire string is affected — voltage drops and the remaining batteries are stressed. Disconnect the string immediately and replace the faulty battery. Ideally replace the entire string if the other batteries are more than 1-2 years old.
