Battery Bank Series/Parallel Configuration
The series/parallel wiring of a battery bank: modules in SERIES add voltages to make the bus, modules in PARALLEL add amp-hours to make capacity. Series count = round(target bus V / module V); four 12.8 V LFP modules in series make a 51.2 V (nominal 48 V) bus, and two strings in parallel give 200 Ah. Usable energy = series x parallel x module V x module Ah x DoD / 1000: a 4S2P bank of 12.8 V / 100 Ah LFP at 80% DoD is 8.19 kWh usable. The actual bus lands on the module nominal (51.2 V), not the 48 V label; never mix chemistries, ages, or capacities on a bus. LFP ~12.8 V/80% DoD, flooded lead-acid ~12.0 V/50%. A configuration aid; the battery/BMS series-parallel limits, the inverter voltage window, and NEC 706 govern.
Formula and source
series_count = max(1, round(target_bus_v / module_v)); actual_bus_v = series_count x module_v; total_ah = parallel x module_ah; usable_kwh = series_count x parallel x module_v x module_ah x DoD / 1000.
Battery bank series/parallel configuration (series adds voltage, parallel adds capacity), by name; the battery/BMS series-parallel limits, the inverter voltage window, and NEC 706 govern.
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