Battery Series/Parallel Calculator
Configure your battery bank voltage and capacity in series and parallel
How to Use This Calculator
- Set the voltage of a single battery (12V, 24V, 48V, or 51.2V LiFePO4).
- Enter the capacity in amp-hours (Ah) of one battery.
- Enter how many batteries you'll wire in series (adds voltage, keeps Ah the same).
- Enter how many strings you'll wire in parallel (adds Ah, keeps voltage the same).
- Read your total bank voltage, capacity, total batteries, and energy in kWh.
Series vs. Parallel Rules
Series: Voltage adds, capacity (Ah) stays the same. Vbank = V × (batteries in series).
Parallel: Capacity (Ah) adds, voltage stays the same. Ahbank = Ah × (batteries in parallel).
Bank Energy (kWh) = Bank Voltage × Bank Ah ÷ 1000
| Config | Single Battery | Bank Voltage | Bank Ah | Bank kWh |
|---|---|---|---|---|
| 4S1P | 12V / 100Ah | 48V | 100 Ah | 4.8 kWh |
| 4S2P | 12V / 100Ah | 48V | 200 Ah | 9.6 kWh |
| 1S4P | 51.2V / 100Ah | 51.2V | 400 Ah | 20.5 kWh |
| 2S4P | 24V / 200Ah | 48V | 800 Ah | 38.4 kWh |
Batteries & Accessories
Frequently Asked Questions
Series or parallel — which is better?
Higher voltage (series) means lower current, so you can use thinner wire and smaller breakers. For systems over 1.5 kW, build a 48V bank. Use parallel only to add capacity once you've reached your target voltage.
Can I mix different batteries?
No. Mixing voltages, capacities, or chemistries causes imbalance, rapid wear, and safety risks. Always use identical batteries and add a BMS per string.
How many batteries can I put in parallel?
Most manufacturers allow up to 4–8 parallel strings. Beyond that, current sharing becomes uneven. For very large banks, use fewer, higher-capacity batteries instead of many parallel small ones.
Battery Configuration Diagrams
Series Configuration (4S1P)
In a series connection, batteries are linked positive-to-negative. Voltage adds up, capacity (Ah) stays the same. Use series to reach your target system voltage (e.g., four 12V batteries in series = 48V).
┌──────┐ ┌──────┐ ┌──────┐ ┌──────┐ │ BAT1 │ │ BAT2 │ │ BAT3 │ │ BAT4 │ │ 12V │ │ 12V │ │ 12V │ │ 12V │ │100Ah │ │100Ah │ │100Ah │ │100Ah │ └──┬─┬─┘ └──┬─┬─┘ └──┬─┬─┘ └──┬─┬─┘ │ │ │ │ │ │ │ │ │ └─────────┘ │ │ │ │ │ │ (to BAT2) │ │ │ │ │ │ │ └─────────┘ │ │ │ │ │ (to BAT3) │ │ │ │ │ │ └─────────┘ │ │ │ │ (to BAT4) │ (+) │ │ (-) OUT OUT 48V | 100Ah | 4.8 kWh
Parallel Configuration (1S4P)
In a parallel connection, all positives are linked together and all negatives are linked together. Capacity (Ah) adds up, voltage stays the same. Use parallel to increase runtime at the same voltage.
(+)───────────────────────────────── (+) OUT │ │ │ │ ┌─┴───┐ ┌─┴───┐ ┌─┴───┐ ┌─┴───┐ │BAT 1│ │BAT 2│ │BAT 3│ │BAT 4│ │51.2V│ │51.2V│ │51.2V│ │51.2V│ │100Ah│ │100Ah│ │100Ah│ │100Ah│ └─┬───┘ └─┬───┘ └─┬───┘ └─┬───┘ │ │ │ │ (-)───────────────────────────────── (-) OUT 51.2V | 400Ah | 20.5 kWh
Series-Parallel Configuration (2S2P)
A combination of series and parallel gives you both higher voltage and higher capacity. This is common for larger systems.
(+)────────────────────── (+) OUT │ │ ┌─┴───┐ ┌───┐ ┌───┐ ┌┴────┐ │BAT 1│─────│BAT│ │BAT│──│BAT 4│ │ 24V │ │ 2 │ │ 3 │ │ 24V │ │200Ah│ │24V│ │24V│ │200Ah│ └─┬───┘ └─┬─┘ └─┬─┘ └─┬───┘ │ │ │ │ (-)────────┴──────┴───────(-) OUT String 1 (Series): BAT1 + BAT2 = 48V / 200Ah String 2 (Series): BAT3 + BAT4 = 48V / 200Ah Parallel: 48V / 400Ah / 19.2 kWh
BMS Considerations for Battery Banks
A Battery Management System (BMS) is essential for LiFePO4 battery banks. The BMS protects against overcharge, over-discharge, over-current, and cell imbalance — critical safety features for any lithium battery installation.
Key BMS Requirements
- Per-string BMS: Each parallel string should have its own BMS to prevent current imbalance between strings
- Cell balancing: Active or passive balancing ensures all cells within a battery reach the same state of charge
- Temperature sensing: BMS must monitor cell temperature to prevent thermal runaway — critical for safety
- Overcurrent protection: BMS should disconnect the battery if current exceeds rated discharge/charge limits
- Communication: CAN bus or RS485 communication allows the inverter to read battery SOC, voltage, and temperature
Parallel String Best Practices
- Use identical batteries — same brand, model, capacity, and age
- Install a DC circuit breaker or fuse per parallel string for isolation
- Use equal-length interconnect cables to balance resistance across strings
- Charge all batteries to 100% before first parallel connection
- Limit parallel strings to manufacturer specifications (typically 4-8 maximum)
- Use busbars for large parallel banks rather than daisy-chaining
- Consider a battery combiner box with individual string fusing
BMS Communication Protocols
| Protocol | Use Case | Common Inverters |
|---|---|---|
| CAN Bus | Most common for LiFePO4 | Sol-Ark, EG4, Schneider |
| RS485 / Modbus | Industrial and rack-mount | Solis, Fortress, Pytes |
| RS232 | Legacy systems | Outback, Magnum |
Recommended Products for Battery Banks
Series vs Parallel — When to Use Each
| Factor | Series | Parallel |
|---|---|---|
| Voltage | Increases (adds) | Stays the same |
| Capacity (Ah) | Stays the same | Increases (adds) |
| Energy (kWh) | Increases | Increases |
| Current draw | Lower (good) | Higher (thicker wire needed) |
| Best for | Reaching target voltage | Adding capacity/runtime |
| Wire size needed | Smaller (thinner) | Larger (thicker) |
Rule of thumb: Always build voltage first with series, then add capacity with parallel. For systems over 1.5 kW, target 48V to minimize current and wire size. See our Battery Sizing Calculator for complete system design.
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