DIY 18650 Powerwall Calculator

Size your DIY lithium-ion battery pack. Enter your cell configuration and get instant energy, voltage, and state-of-charge calculations.

Uses standard 18650 Li-Ion cell specs: 3.7V nominal, 4.2V full, 2.8V cutoff.

Cells in Series

Cells in Parallel

Avg Cell Capacity

mAh

Number of Packs

—

Total Energy

—

Cells Needed

—

Pack Capacity

Ah at nominal V

—

Nominal Voltage

25%

50%

75%

100%

Cell Max Discharge

Wire Run Distance

feet

Click a tab, then "Calculate" after running the pack calculator.

Run the pack calculator first to see fuse/breaker recommendations.

Config	Nominal V	Typical Use	Energy (3000mAh cells)
7S	25.9V	E-bikes (24V), power tools	—
10S	37.0V	E-bikes (36V), e-scooters	—
13S	48.1V	E-bikes (48V), DIY powerwalls	—
14S	51.8V	48V solar systems, powerwalls	—
16S	59.2V	High-voltage powerwalls	—

Energy column updates when you calculate a pack with matching series count.

Always use a BMS (Battery Management System) – it protects against overcharge, over-discharge, overcurrent, and cell imbalance.
Use fused wiring – size your fuses to the max continuous discharge of your pack.
Match cells – use cells of the same brand, model, and ideally capacity-tested within 50mAh of each other.
Spot-weld, don't solder – soldering overheats cells and damages them. Use a spot welder with nickel strip.
Ventilation – 18650 cells can vent hot gas if abused. Ensure your enclosure has ventilation.

Looking for pre-built LiFePO4 batteries instead?