Off-Grid Battery Calculator
Off-grid battery sizing is mainly about matching your real daily energy use to enough stored energy for the number of backup days you want. A good calculator helps turn daily watt-hours, autonomy days, voltage, and battery depth of discharge into a practical battery bank size for cabins, homes, farms, and remote buildings.
This page is built for complete off-grid planning. It estimates required battery capacity in amp-hours and kilowatt-hours, shows how many standard battery modules you may need, and highlights why 48V systems are usually the better choice once loads move beyond very small cabins or weekend setups.
Short answer: Off-grid battery size is commonly estimated with Required Ah = Daily Load Wh × Autonomy Days ÷ Voltage ÷ DoD. For most modern lithium systems, 48V and LiFePO4 are the most practical default starting points.
Off-Grid Battery Sizing Tool
Estimate required battery bank size for off-grid homes, cabins, farms, and backup-ready solar systems
Off-Grid Battery Sizing Steps
Step 1: Daily Load
Calculate your total daily load in watt-hours. This is the foundation of the whole design and should include lights, appliances, pumps, electronics, and inverter-powered loads.
Step 2: Autonomy
Choose how many days of backup you want without charging. One to three days is common for many off-grid systems, but remote and weather-sensitive sites may need more.
Step 3: DoD
Select a realistic depth of discharge. LiFePO4 is often sized around 80% usable DoD in practical off-grid planning, while lead-acid usually needs more conservative limits.
Step 4: Voltage
Choose your system voltage. 48V is usually recommended for off-grid homes and larger systems because it reduces current and makes wiring more manageable.
Step 5: Required Ah
Use the formula Required Ah = Wh × days ÷ V ÷ DoD, then round up for safety margin, aging, and future load growth.
Battery Formula
The core off-grid battery formula is:
Required Ah = Daily Load Wh × Autonomy Days ÷ Voltage ÷ DoD
In practice, many designers also add a reserve margin because real systems are affected by inverter losses, weather changes, battery aging, and load growth. This calculator lets you add extra headroom so the result is more practical than a bare theoretical minimum.
For example, if you use 4000Wh per day, want 2 days of autonomy, use a 48V system, and assume 80% DoD, the battery size is 4000 × 2 ÷ 48 ÷ 0.80 = 208.3Ah before any extra reserve margin is added.
| System Type | Typical Battery Bank | Nominal Energy |
|---|---|---|
| Small cabin | 48V 100Ah | 4.8kWh |
| Medium home | 48V 200Ah | 9.6kWh |
| Large home | 48V 400Ah | 19.2kWh |
| Farm | 48V 600–1000Ah | 29–48kWh |
Typical Off-Grid Systems
Small Cabin
A small cabin with modest energy use may work well with a 48V 100Ah LiFePO4 battery, which stores about 4.8kWh nominal.
Medium Home
A medium off-grid home often starts around 48V 200Ah, which is about 9.6kWh nominal and suits lighter everyday living or partial backup.
Large Home
A larger home with heavier daily use may need around 48V 400Ah, or about 19.2kWh nominal, especially when autonomy expectations are higher.
Farm Systems
Farms and high-demand properties may need around 48V 600Ah to 1000Ah, which translates to roughly 29kWh to 48kWh of nominal storage.
Why 48V Is Recommended
As off-grid systems get larger, battery current rises quickly if the voltage stays low. A higher system voltage reduces current for the same power level, which usually means smaller cable requirements, lower losses, and easier inverter integration. That is why 48V is widely considered the standard choice for modern off-grid homes and larger battery banks.
For example, the same power draw that feels manageable at 48V may become impractical at 12V because the current is four times higher. Small cabins can still use 12V or 24V systems, but most full-time off-grid homes benefit from moving to 48V once the battery bank and inverter size become substantial.
Practical warning: If you are sizing for a full-time home, larger inverter, pump loads, or future expansion, 48V is usually the better long-term path. Smaller voltages can become inefficient and cumbersome as the system grows.
Is LiFePO4 Best for Off-Grid?
For most modern off-grid systems, LiFePO4 is the preferred battery chemistry because it offers long cycle life, strong usable depth of discharge, low maintenance, and better practical efficiency than lead-acid. It also makes battery banks smaller for the same usable energy because more of the rated capacity can be used safely in everyday operation.
Lead-acid still has some budget and legacy use cases, but it generally needs a much larger nominal bank to provide the same usable energy. That is why many off-grid homeowners choose LiFePO4 when they want compact storage, lower maintenance, and a better long-term system.
Practical rule: Think in kWh first, then convert to Ah at the chosen voltage. kWh usually makes off-grid planning easier because daily loads, autonomy, and battery-bank comparisons all become clearer.