Lithium Battery Calculator
Size your LFP, NMC, or NCA battery bank — get capacity, cell count, and weight estimate.
Cell count based on standard 100Ah LFP prismatic cells. Actual configuration depends on available cell sizes. A BMS sized for 48V / 123Ah is required.
How to Use This Calculator
Enter your daily energy usage
Input your daily energy consumption in kWh. For an off-grid home, add up all your appliances: refrigerator (~1.5 kWh), LED lighting (~0.5 kWh), laptop (~0.1 kWh), TV (~0.2 kWh), etc. For a grid-tied storage system, you might only want to cover essentials during outages — perhaps 3-5 kWh/day. The average US home uses ~28 kWh/day, but off-grid systems typically run 3-10 kWh/day with energy-efficient appliances.
Set days of autonomy
Days of autonomy is how long your batteries can power your home without solar charging. 1 day covers overnight and short cloudy periods. 2-3 days handles most weather-related outages. More than 3 days adds significant cost and weight with diminishing returns — it's usually better to oversize the solar array instead.
Choose cell chemistry and system voltage
For home energy storage, LFP (LiFePO4) is the clear choice — 3,000-5,000+ cycle life, no thermal runaway risk, and 10+ year service life. NMC (used in EV batteries) has higher energy density but shorter cycle life (~1,000-2,000 cycles) and requires more active thermal management. 48V is the standard for residential systems — lower current reduces cable sizing costs and improves inverter efficiency.
Adjust Depth of Discharge
Depth of Discharge (DoD) determines what fraction of battery capacity you actually use. At 85% DoD, a 10 kWh battery provides 8.5 kWh of usable energy. Higher DoD means more usable energy from the same battery, but slightly fewer total cycles. The calculator adjusts total required capacity to account for your selected DoD.
The Formula
The series configuration sets the system voltage. For a 48V LFP system (3.2V cells): 48 ÷ 3.2 = 15 cells in series (often written 16S since 16 × 3.0V nominal = 48V). The parallel configuration multiplies capacity. Two strings in parallel doubles the Ah capacity at the same voltage.
Weight is estimated from the cell's energy density. LFP is the heaviest lithium chemistry at ~140 Wh/kg. NMC is lighter at ~200 Wh/kg. A 10 kWh LFP bank weighs approximately 71 kg (157 lbs).
Example
Off-grid cabin: 5 kWh/day, 2-day autonomy, 48V LFP
A cabin owner uses 5 kWh/day and wants 2 days of autonomy to handle cloudy weather. They choose LFP chemistry at 48V for safety and longevity.
Results
The 16S3P configuration is standard for 48V off-grid LFP systems. This bank stores 15.36 kWh, providing 13 kWh of usable energy at 85% DoD — comfortably covering the 10 kWh needed for 2 days. A 48V 300Ah BMS is required to protect the cells from overcharge, over-discharge, and overcurrent.