Battery Bank Wiring Instrument
IEEE 485 & NEC 706 REFERENCE METHODOLOGYTurn a target bank size into a wireable series-parallel configuration — series count, parallel strings, total batteries, bank voltage, Ah and kWh — with interactive SVG topological wiring.
Battery bank sizing, from target to wiring
A battery bank is two decisions made physical: how many batteries in series it takes to reach your system voltage, and how many identical series strings in parallel it takes to reach your target capacity. This battery bank calculator makes both decisions for you, reports the resulting bank voltage, Ah, and kWh, and draws the exact wiring — including which terminal of each battery connects to which.
It applies no chemistry assumptions and no safety factors — the configuration you see is the configuration you would build. If you instead want to size a solar bank from daily energy use and autonomy (with depth of discharge and inverter efficiency), use the Solar Battery Calculator.
Formulas
The bank sizing math
Straightforward arithmetic with two constraints: whole batteries only, and battery voltage must divide system voltage.
series = system voltage ÷ battery voltage
Wiring batteries in series increases voltage while keeping capacity (Ah) the same: four 12 V 100 Ah batteries in series give 48 V at 100 Ah.
strings = ⌈target Ah ÷ battery Ah⌉
Wiring identical series strings in parallel increases capacity. Always rounded up so the bank never falls short of the target.
Frequently asked questions
How do I calculate a battery bank configuration?
Divide the system voltage by one battery's voltage to get the number of batteries in series. Divide the target bank amp-hours by one battery's amp-hours and round up to get the number of parallel strings. Total batteries = series × strings, bank Ah = strings × battery Ah, and bank energy (Wh) = bank Ah × bank voltage.
What does 2S2P, 4S1P, or 4S4P mean?
The notation is series count first, parallel strings second. 2S2P means two batteries in series per string and two strings in parallel — 4 batteries total. 4S1P is one series string of four (no parallel doubling), and 4S4P is four batteries in series in each of four parallel strings — 16 batteries total.
Does wiring batteries in series increase amp-hours?
No. Series wiring increases voltage only — amp-hours stay the same. Parallel wiring increases amp-hours but keeps the voltage. To raise both, batteries are wired in series to reach the system voltage, and identical series strings are then wired in parallel.
How many batteries do I need for a 48V system?
For 12 V batteries, four in series per string. The number of parallel strings depends on the capacity you need: a 10 kWh (10,000 Wh) target at 48 V is about 208 Ah, so one string of 200 Ah batteries rounds up to two strings — 8 × 12 V 200 Ah batteries (4S2P) in total.
Does this calculator account for depth of discharge?
No — and deliberately so. This tool converts a stated target into a physical configuration; it applies no chemistry assumptions. If you are sizing a solar bank from daily energy use and autonomy, use the Solar Battery Calculator, which applies chemistry-based depth of discharge and inverter efficiency with documented bases.
Related Calculators
Continue your system design with the other tools in the SolarCalcKit suite — in the order the rest of your design flows: load audit → battery → bank wiring → MPPT → wire size → inverter.
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Start by auditing daily appliance energy use (Wh & kWh) and connected load.
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Size a battery bank from that daily energy, autonomy days, chemistry and depth of discharge.
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Size an inverter from continuous and surge loads, with DC battery current.
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