How to connect batteries in series and in parallel

September 28, 2026 · 5 min read · Danilo Nascimento

Learn what happens to voltage, current and capacity when you connect batteries in series, in parallel or both, with examples and practical precautions.

Why it matters

A single 12 V, 100 Ah battery stores little for a home. To reach the voltage the inverter needs and the energy for a whole night, batteries are combined in series, in parallel or both. The layout changes voltage and capacity, but not the sum of the batteries’ nominal energy; the energy actually delivered depends on the conditions of use.

1.2 kWhone 12 V, 100 Ah battery

× 4identical batteries

4.8 kWhbank energy, in series or in parallel

Series vs parallel

In series

Adds up the voltage

Voltage: 4 × 12 V = 48 V
Capacity: stays at 100 Ah
Energy: 48 V × 100 Ah = 4.8 kWh
The + terminal of one battery goes to the − of the next

In parallel

Adds up the capacity

Voltage: stays at 12 V
Capacity: 4 × 100 Ah = 400 Ah
Energy: 12 V × 400 Ah = 4.8 kWh
All + terminals joined together, and all − terminals too

The same four batteries, two layouts: the energy is the same; what changes is how it is delivered.

The terminals left over, the negative of the first battery and the positive of the last, go to the inverter or the charge controller.

Series-parallel: combine both

Larger banks mix both connections. Two series of two batteries connected in parallel make a 2S2P bank: 24 V and 200 Ah. The energy of any layout comes from the same calculation:

48 Vvoltage×100 Ahcapacity÷1,000Wh → kWh=4.8 kWhenergy

Why larger systems prefer 48 V

Power is voltage times current (P = V × I). For the same power, the higher the voltage, the lower the current flowing through the cables.

Ideal current for 2,000 W DC, with no conversion losses (the inverter’s real current is higher)

12 V bank167 A

24 V bank83 A

48 V bank42 A

Precautions and common mistakes

Do

Use identical batteries: same chemistry, model, capacity, age and manufacturer
Fully charge all of them (or equalize their voltage) before connecting them
In parallel, use cables of the same length and cross-section
In parallel, take the + from the first battery and the − from the last (diagonal output, one of the options; in larger banks, busbars balance the current better)
Install a DC fuse or circuit breaker next to the bank positive
With lithium, check in the manual how many units the BMS allows in series and in parallel

Avoid

Mixing new and used batteries: the weakest one limits the others
Adding up voltage and capacity at the same time: “48 V 400 Ah” with four batteries does not exist
Connecting + to + in a series: the voltages cancel out
Taking + and − from the same battery in parallel: that battery ages first
Thin cables or loose terminals: they heat up and melt the posts

Drawing your bank

Before buying cables and terminals, draw the bank. The diagram below, made in Editor Solar itself, shows both layouts side by side for you to adapt.

Draw it in Editor Solar

This is Editor Solar itself, already loaded with the diagram from this article. Move the equipment, edit labels, connect new parts and export to PNG, SVG or PDF. It is free and runs right in your browser.

Four 12 V, 100 Ah batteries in series (top) and in parallel (bottom), with the positives on one busbar and the negatives on the other.

Try it: Turn the bottom bank into 2S2P: connect batteries 5 and 6 in series, then 7 and 8, and take the free positive of each series to the + busbar and the free negative to the − busbar. Label the result “24 V · 200 Ah”.

Ready-made templates: Solar system with battery diagram (no grid) · Hybrid solar and wind system diagram

Open this diagram in the full editor ↗

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