Battery Pack Configuration
Series × parallel cells → pack voltage, capacity, and watt-hours.
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The engineering
Series stacks voltage, parallel stacks capacity, and energy — the honest number — is their product. A '13S4P' e-bike pack of 3.6 V / 3.4 Ah cells is 46.8 V, 13.6 Ah, 636 Wh regardless of how the marketing rounds it. Compare packs in watt-hours; voltage and amp-hours alone are each half a spec.
Real packs derate the arithmetic: series strings are only as good as their weakest cell (hence balancing circuits in every lithium BMS), nominal voltage is a curve's midpoint rather than what the terminals read, and mixing aged and fresh cells in parallel invites the good ones to carry — and quietly cook for — the bad ones.
Where this math comes from
The very first battery was a series stack — Volta's 1800 pile literally piled zinc-silver cells to multiply voltage, and 'battery' (borrowed from artillery) meant the grouping, not the cell. Planté's 1859 lead-acid made the stack rechargeable, and the 6-cell, 12-volt series string under every car hood is his arithmetic fossilized.
Sony's 1991 commercialization of the lithium-ion 18650 turned pack configuration into a consumer-scale discipline: laptop 3S2P bricks, then Tesla's early ~7,000-cell EV packs, all of it S×P bookkeeping on the same cylindrical cell.
- 1800Alessandro VoltaThe pile — cells in series, the first battery.
- 1859Gaston PlantéLead-acid rechargeable cell; the 12 V series string to come.
- 1991SonyLi-ion 18650 commercialized — S×P becomes everyone's math.
See the full timeline of the math behind every calculator →
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