Calculate the battery pack size needed for your project, including energy capacity, cell count, and estimated weight.
2026-03-28T00:00:00Z
60 Wh
Energy Capacity Needed
Energy Equivalent:
~5 × 18650 cells (energy-only estimate, configuration not determined)
Note: This is purely based on total Wh needed. Actual pack requires series/parallel design and voltage matching. Do not use for production.
Battery sizing determines the energy capacity (Wh) and physical specifications needed to power a system for a desired runtime. The calculation is based on the system voltage, current draw, and required operating time. Proper battery sizing ensures reliable operation while optimizing for size, weight, and cost.
Important Notes: This calculator assumes 18650 cells (~12.5 Wh average rating) and a uniform series configuration. Real 18650 cells vary (10.5–15 Wh depending on model); verify against actual cell specs. The weight estimate (~48g per cell) is approximate. For production designs, always validate against real component datasheets and consider voltage matching (e.g., 3.7V nominal per cell).
This tool provides an initial estimate only. Before manufacturing, validate with real component datasheets, test your system under expected conditions, and consider safety margins for environmental variations and component aging.
Size a battery pack for a 12V system drawing 500 mA that needs 10 hours of runtime:
Series connection (3S): 3.7V + 3.7V + 3.7V = 11.1V, same capacity. Parallel (3P): 3.7V stays 3.7V, capacity triples. Use series for voltage, parallel for capacity. Example: 3S5P = 11.1V, 5× the capacity of one cell.
18650 cells are standardized (18mm × 65mm), widely available, affordable, and well-documented. Common capacities: 2600-3500 mAh (9.6-13 Wh at 3.7V nominal). Alternatives: 26650 (larger), 18350 (smaller), LiPo pouches (flexible shapes), prismatic cells (custom).
Series determines voltage, parallel determines capacity. For desired voltage V and single-cell 3.7V: series_count = V ÷ 3.7, rounded up. For desired Ah: parallel_count = Ah_needed ÷ Ah_per_cell, rounded up. Example: 12V system needing 5 Ah → 3S5P (3 series × 5 parallel).
Wh = mAh × Voltage ÷ 1000. Most 18650 cells: 3000 mAh × 3.7V = 11.1 Wh. High-capacity cells (3500 mAh): 13 Wh. Lower quality (2600 mAh): 9.6 Wh. Always check the datasheet for the specific cell model.
Only for parallel connections. Parallel adds capacity (3 cells at 3000 mAh each in parallel = 9000 mAh total at same voltage). Series does NOT add capacity or voltage in simple addition—use the series/parallel configuration formulas above.
BMS (Battery Management System) monitors cell voltage, balances charge, protects against over-charge/discharge, and prevents thermal runaway. Essential for all multi-cell Li-ion packs, especially 3S+ (higher voltages). BMS adds cost but prevents fires and extends battery life.
Depends on configuration complexity and volume. Simple series packs: low cost. Complex parallel-series (e.g., 10S20P) with balancing BMS: expensive and requires spot-welding equipment. Consider buying pre-assembled packs for small quantities; custom assembly for high volumes.
Actual 18650 weight varies: standard cells 42-48g, high-capacity cells 50-52g, low-quality 45g. The estimate uses 48g average. BMS, casing, and connectors add 30-100g depending on design. Always weigh prototypes to validate.
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