Solar
Battery Bank Calculator
Series batteries add voltage while parallel strings add amp-hour capacity. Total nominal energy equals bank voltage multiplied by bank amp-hours.
Calculate series/parallel battery quantity, bank voltage, amp-hours, and watt-hours from unit specifications.
Calculated result
Battery bank totals
Calculating…
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Planning math only. Verify equipment specifications and installation requirements separately.
Equipment planning
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Calculate above to generate a parts requirement.
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Data provenance: NLR PVWatts v8 grid awaiting its first private-key refresh; the visible peak-sun-hours fallback is active. EIA residential state averages updated 2026-08-13. ZIP centroids use the 2025 Census Gazetteer. No ZIP or calculator input is sent to those sources. Read the solar data provenance and limitations.
What this calculator returns
Use identical compatible units and follow manufacturer requirements for series/parallel connection and protection.
Formula and variables
The calculation runs entirely in your browser. Static formulas, definitions, examples, and tables remain readable without JavaScript.
Vbank = Vunit × series; Ahbank = Ahunit × parallel; Whbank = Vbank × Ahbank.
- V
- Nominal battery or bank voltage.
- Ah
- Charge capacity in amp-hours.
- Wh
- Nominal or usable stored energy in watt-hours.
- W
- Average load power in watts.
- η
- Entered conversion efficiency.
Total quantity equals series count times parallel-string count.
Worked example
| Input | Value |
|---|---|
| Unit voltage | 12 V |
| Unit capacity | 100 Ah |
| Units in series | 2 |
| Parallel strings | 2 |
Four 12 V, 100 Ah batteries arranged 2S2P create a nominal 24 V, 200 Ah, 4.8 kWh bank.
Reference table
| Appliance | Planning watts | Use note |
|---|---|---|
| LED lamp | 10 W | Nominal example |
| Laptop computer | 60–120 W | Typical planning range |
| Refrigerator while running | 100–250 W | Cycling load; startup can be higher |
| Microwave oven | 900–1,500 W | Input varies by model |
| Portable space heater | 1,500 W | Common high setting |
| Electric kettle | 1,200–1,800 W | Varies by market and model |
Frequently asked questions
What changes when batteries are connected in series?
Series connection adds voltage while the amp-hour capacity remains that of one identical unit.
What changes when batteries are connected in parallel?
Parallel strings add amp-hour capacity while bank voltage remains the voltage of one series string.
Assumptions and limitations
- Nominal energy only.
- No charging, BMS, conductor, fuse, or chemistry safety recommendation.
Method and sources
Review the solar data sources, calculation methodology, and electrical formulas for the references most relevant to this calculation. The broader technical sources index records source scope and verification. Last reviewed .