Series and Parallel Battery Calculator
Enter one cell or battery voltage and amp-hours, plus how many you wire in series and in parallel, to find the resulting pack voltage, amp-hours and total watt-hours.
Results are estimates for planning and education, based on your inputs and standard engineering values (AWG resistance, NEC ampacity, resistivity). Electrical work can be dangerous and is governed by the NEC and your local code — verify all sizing with a licensed electrician and your authority having jurisdiction (AHJ). Not a substitute for professional design.
Calculator
| Pack voltage | 24 V |
|---|---|
| Pack amp-hours | 200 Ah |
| Pack energy | 4,800 Wh |
Formula
Series adds voltage: pack V = cell V × number in series. Parallel adds amp-hours: pack Ah = cell Ah × number of parallel strings. Pack energy in Wh = pack V × pack Ah.
Worked example
Four 12 V 100 Ah batteries in a 2-series, 2-parallel (2S2P) arrangement: pack voltage = 12 × 2 = 24 V; pack capacity = 100 × 2 = 200 Ah; energy = 24 × 200 = 4,800 Wh. The energy is the same no matter how you arrange them, but the voltage and amp-hours differ.
Frequently asked questions
What does wiring in series do?
Series wiring connects the positive of one battery to the negative of the next, adding their voltages while the amp-hours stay the same. Two 12 V 100 Ah batteries in series make a 24 V 100 Ah pack. This is how you build a 24 or 48 V bank from 12 V batteries, which lets the system run at lower current for the same power. All batteries in a series string should be identical and well matched, since the weakest one limits the whole string.
What does wiring in parallel do?
Parallel wiring connects all the positives together and all the negatives together, adding amp-hours while the voltage stays the same. Two 12 V 100 Ah batteries in parallel make a 12 V 200 Ah pack with twice the capacity and runtime. Parallel strings should use identical batteries and balanced cabling so each string shares current evenly; uneven connections cause one string to work harder and age faster.
What does 2S2P mean?
It is shorthand for the arrangement: 2S means two batteries in series, and 2P means two such series strings in parallel, for four batteries total. With 12 V 100 Ah units, 2S2P gives 24 V and 200 Ah. The notation generalizes: 4S2P is eight batteries as two strings of four in series, and so on. Series multiplies voltage, parallel multiplies capacity, and the product of the two counts is the total number of batteries.
Does the arrangement change total energy?
No. The total stored energy depends only on how many batteries you have and their individual capacity, not on how you wire them. Four 12 V 100 Ah batteries always hold about 4,800 Wh whether they are 2S2P at 24 V 200 Ah, all in series at 48 V 100 Ah, or all in parallel at 12 V 400 Ah. The wiring only sets the voltage and amp-hours, which you choose to match your inverter and charge controller.
Can I mix old and new batteries?
It is strongly discouraged. Mixing batteries of different age, capacity, brand or chemistry causes uneven charging and discharging, so the weakest battery is overworked and the whole bank underperforms and ages prematurely. Always build a bank from identical batteries bought together, and replace the entire bank rather than a single cell when it wears out. For lithium banks, also follow the manufacturer guidance on series and parallel limits and battery-management protection.
Source: Series adds voltage, parallel adds amp-hours: pack V = cell V × series; pack Ah = cell Ah × parallel; energy = V × Ah. · All sources