Can I mix different battery brands in the same bank?

Never mix batteries with different capacities, voltages, or ages. Mismatched batteries charge at different rates causing premature failure. Always use identical batteries.

Battery Series/Parallel Calculator

How do you wire your battery bank for target voltage and capacity? Enter your specs — get series count, parallel strings, and wiring instructions.

Target bank specs

Target bank voltage?

Target bank capacity?

Individual battery specs

Battery voltage?

Battery capacity?

Battery bank configuration

4S2P — 8 batteries

Batteries in series (per string)4 batteries

Parallel strings2 strings

Total batteries8 batteries

Bank voltage48 V

Bank capacity200 Ah

Total kWh9.6 kWh

Wiring: Build 2 series strings of 4 batteries each. Within each string, connect + to - in series to reach 48V. Then connect all strings in parallel (all string positives together, all negatives together). Use a bus bar and equal-length cables. Total: 8 batteries in a 4S2P configuration.

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How to Use This Calculator

Set your target bank specs

Choose your target bank voltage from the dropdown (12V, 24V, or 48V) and enter the target capacity in amp-hours. The voltage determines how many batteries you'll wire in series; the Ah determines how many parallel strings you need.

Enter individual battery specs

Enter the voltage and Ah rating of each individual battery you're using. These are printed on the battery label. Common examples: a 12V 100Ah LiFePO4 battery, a 12V 200Ah AGM battery, or a 6V 225Ah golf cart battery.

Read the configuration

The result shows your configuration in standard notation (e.g., 4S2P means 4 batteries in series, 2 parallel strings = 8 total batteries). The wiring description tells you exactly how to connect them. Use this alongside the total kWh result to verify you're meeting your storage goal.

The Formula

Series count = Target voltage ÷ Battery voltage Parallel count = ceil(Target Ah ÷ Battery Ah) Total batteries = Series count × Parallel count Bank voltage = Series count × Battery voltage Bank Ah = Parallel count × Battery Ah Total kWh = Bank voltage × Bank Ah ÷ 1000

Series wiring adds voltages while keeping Ah constant. Parallel wiring adds Ah (capacity) while keeping voltage constant. Combining both lets you reach any target voltage and capacity using standard batteries.

The 4S2P notation is standard shorthand: S = series (voltage multiplier), P = parallel (Ah multiplier). A 4S2P bank of 12V 100Ah batteries gives 48V, 200Ah = 9.6 kWh.

Example

Building a 48V 400Ah LiFePO4 battery bank

An off-grid homeowner wants a 48V 400Ah battery bank (19.2 kWh) using standard 12V 100Ah LiFePO4 batteries. What configuration do they need?

Target voltage48V

Target capacity400 Ah

Battery specs12V 100Ah each

Configuration

Series count4 batteries (48V ÷ 12V)

Parallel count4 strings (400Ah ÷ 100Ah)

Total batteries16 batteries (4S4P)

Total kWh19.2 kWh

The wiring: Build 4 series strings of 4 batteries each (connecting + to - in sequence to reach 48V per string). Then connect all 4 strings in parallel using bus bars — all positive terminals to positive bus, all negative to negative bus. Equal-length cables are essential for balanced charge/discharge across all strings.

FAQ

What voltage should I choose for my battery bank? ▼

48V is almost always best for home and off-grid systems above 3 kWh. Higher voltage means lower current for the same power, which means smaller wire sizes, less heat, and greater efficiency. A 1,000W inverter at 48V draws ~21A; at 12V it draws ~83A — requiring wire 4x thicker. 12V is only practical for very small systems (RVs, small boats) under 2-3 kWh. 24V is a middle ground for medium cabins. Modern MPPT charge controllers and inverters work at all three voltages.

Can I mix different battery brands or ages in the same bank? ▼

Never mix batteries with different capacities, voltages, or ages in the same bank — especially in series strings. Mismatched batteries charge and discharge at different rates, causing over/under-charging and premature failure of the weakest battery. The worst battery limits the entire bank's performance. Always use identical batteries (same brand, model, age, and capacity). If one battery fails, replace the entire string or buy a battery with matching internal resistance.

Why do I need equal-length cables in a parallel battery bank? ▼

Unequal cable lengths create unequal resistance between parallel strings. Lower resistance strings carry more current, causing uneven charge/discharge rates across batteries. Over time, this imbalances the batteries and shortens their life. The solution: use identical cable lengths between each string and the bus bars. Many installers use the "cross-pattern" or "series-symmetric" connection method to ensure equal path lengths even with physically offset batteries.

How do I connect 6V golf cart batteries to make 12V or 24V? ▼

6V golf cart batteries (typically 200-250Ah each) are a popular low-cost option. To make 12V: connect 2 batteries in series (6V + 6V). To make 24V: connect 4 in series. To make 48V: connect 8 in series. For more capacity, connect those series strings in parallel. Enter 6 in the battery voltage field and your golf cart battery's Ah rating to configure your bank. Trojan T-105 batteries are 6V 225Ah — popular for off-grid.

What is the maximum number of parallel strings recommended? ▼

Most manufacturers and installers recommend a maximum of 4 parallel strings for lead-acid batteries. Beyond that, balancing current distribution becomes increasingly difficult. For LiFePO4 batteries with a built-in BMS, up to 6-8 parallel strings is sometimes used, but 4 or fewer is preferred for long-term reliability. If you need more capacity than 4 strings allows, upgrade to larger individual batteries rather than adding more parallel strings.