A battery’s energy is watt-hours, not milliamp-hours: Wh = (capacity in Ah) × the nominal voltage. A 3000 mAh, 3.7 V cell holds 11.1 Wh. Stack them into a pack and a 3S2P of those cells holds 66.6 Wh at 11.1 V. Set your own below.
Inputs
Result
66.6 Wh
pack energy (3S2P)
Watt-hours, not mAh, is what compares packs of different voltages and what shipping rules go by.
Pack voltage
11.1 V nominal
Pack capacity
6000 mAh
Series adds volts, parallel adds capacity
A pack is written S×P: S cells in series stack their voltages, P cells in parallel add their capacities. Energy is the product of the two, so a 3S2P and a 2S3P of the same cells hold the same watt-hours but at different voltage and current. Use watt-hours to compare them, because mAh alone is meaningless across different voltages: 2000 mAh at 12 V is far more energy than 2000 mAh at 3.7 V.
Why watt-hours is the number that matters
Watt-hours is what sets runtime (energy divided by the load’s power), what sizes a charger, and what the shipping and airline rules go by, since they cap watt-hours per cell and per pack. Capacity in mAh only tells you the story once you also fix the voltage.
From a real board
The OTD l3-04 board is a multi-cell battery management system: it charges and protects a pack whose energy you size exactly this way (One Thousand Drones, curriculum 2026). A bigger pack stores more energy and also more to go wrong, which is the whole reason a BMS watches every cell. See the BMS course, or start with the single-cell battery and power module.
References
- Your cell’s datasheet for the rated capacity and the nominal voltage (and the watt-hour figure, if it lists one).
- One Thousand Drones. Multi-cell battery management system (l3-04). Build the board.