Batteries — 24V, 36V and 48V packs

Pack	Nominal	Capacity	Discharge	Charger	Links
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Voltage classes, in plain numbers

Class	Chemistry / config	Nominal	Full charge	Cutoff
24 V	7S Li-ion, or 8S LiFePO4, or 2×12 V lead	24.0 / 25.6 / 24.0	29.4 / 29.2 / 29.4	21.0 / 20.0 / 21.0
36 V	10S Li-ion, or 2×18 V tool packs in series	36.0	42.0	30.0
48 V	13S Li-ion, or 16S LiFePO4	48.0 / 51.2	54.6 / 58.4	39.0 / 40.0

Two 18 V tool packs in series is 36 V nominal, 42 V hot, and the Ah does not double. Series adds voltage and keeps capacity; parallel adds capacity and keeps voltage. Builders get this backwards constantly, then wonder why runtime did not improve.

Sizing the pack to the board

Current first. Board watts ÷ nominal volts ÷ 0.88 (class-D efficiency) = amps at full tilt. The BMS continuous rating should exceed that with margin, not match it.
Energy second. Watt-hours ÷ average draw = hours. Music average draw is roughly a quarter to a third of the full-tilt number.
Chemistry third. LiFePO4 tolerates abuse and cold better and has a flatter discharge; Li-ion is lighter per Wh. Lead is cheap, heavy, and sags.