A cabin battery bank should not be sized around the lights you plan to use. Size it around the loads that could disrupt the cabin, such as a well pump at dawn, a microwave, or a space heater. The battery, the inverter, and the charging sources have to work as one system that provides usable power when solar output drops.
To size an off grid cabin battery system, add up your daily energy use in kWh, multiply it by the days of storage you want, and divide by usable depth of discharge. A cabin using 6 kWh per day with two days of autonomy needs about 15 kWh of nominal LiFePO4 capacity at 80% depth of discharge.
This guide walks through each step, from your load list to voltage, inverter, solar, and winter planning, so your off grid solar system with batteries is sized for the cabin you actually have. Browse our Off-Grid Battery Systems.
Start With Daily Energy, Not Battery Voltage
Begin with a load list. Multiply each device’s watts by its daily run hours to get watt-hours, then divide by 1,000 for kWh. A small weekend cabin uses about 2 to 4 kWh per day. A larger cabin with a full-size refrigerator, washer, or mini-split can reach 8 to 15 kWh per day. The Solar Battery Sizing Calculator can run your load list for you.
Electric resistance heat, water heating, and cooking can push demand much higher and require a much larger array, battery bank, and inverter. Measure actual use with a plug-in power meter where you can. For hardwired equipment, use manufacturer ratings and plan conservatively.
Choose How Many Days of Storage You Need
Days of autonomy is how long the cabin can run on the battery alone. As a guide, 1 to 2 days suits a lightly used cabin with a generator. 2 to 3 days suits regular use or limited winter solar. Remote sites that are hard to reach in bad weather may need more.
Use this formula: daily energy × days of autonomy ÷ usable depth of discharge = nominal capacity.
For example, 6 kWh per day × 2 days = 12 kWh. Divide by 0.80 for 80% depth of discharge, and the target battery bank is about 15 kWh of nominal capacity.
BigBattery’s NEXUS 2 + EG4 6000XP off-grid system pairs a 16.1 kWh battery with a 6kW inverter, which fits that target.
Battery Size by Daily Use and Days of Storage
Nominal capacity at 80% usable depth of discharge.
| Daily energy use | 1 day of storage | 2 days of storage | 3 days of storage |
|---|---|---|---|
| 3 kWh | 3.75 kWh | 7.5 kWh | 11.25 kWh |
| 6 kWh | 7.5 kWh | 15 kWh | 22.5 kWh |
| 10 kWh | 12.5 kWh | 25 kWh | 37.5 kWh |
LiFePO4 batteries offer high usable capacity, fast charging, and long life, with 4,000 or more cycles under appropriate conditions. Operating with margin also protects battery life.
12V, 24V, or 48V for an Off Grid Cabin Battery System?
Higher voltage delivers the same power at lower current, which allows smaller cable and less voltage drop. 12V suits very small cabins with inverters under roughly 2,000 watts, because current and cable requirements rise quickly as the system grows. 24V is a middle option for inverters of 2,000 to 4,000 watts if loads are managed carefully.
For most full-time or expansion-minded cabins, 48V is the cleaner choice. It has lower DC current and works with many residential solar components, including a 48V off grid inverter.
Which System Voltage Fits Your Cabin?
| System voltage | Best for | BigBattery example |
|---|---|---|
| 12V | A very small cabin with modest DC loads and an inverter under roughly 2,000 watts | Husky 2 12V off-grid system (5.12 kWh) |
| 24V | A compact cabin with 2,000 to 4,000 watts of inverter power | Husky 2 24V off-grid system (5.12 kWh) |
| 48V | A full-time or expansion-minded cabin | NEXUS 2 + EG4 6000XP (16.1 kWh, 6kW) |
Voltage alone does not measure stored energy. Capacity comes from nominal voltage multiplied by amp-hours. LiFePO4 batteries run slightly above their label, at 51.2V nominal for 48V and 12.8V nominal for 12V, so a 48V, 100Ah battery stores about 5.12 kWh, while a 12V, 100Ah battery stores about 1.28 kWh.
Size the Inverter for Running Loads and Startup Surges
The continuous inverter rating must cover the loads that run at the same time. The surge rating must handle motor startup demand from pumps, compressors, and shop tools. A 3,000-watt inverter may suit a simple cabin, but motors can briefly draw several times their running wattage. Starting a pump while a microwave and coffee maker run can overload the inverter or trigger battery protection.
Map your realistic simultaneous loads, then choose an off grid inverter with headroom for both continuous and surge demand. Confirm the battery can supply the required DC current.
Pure sine wave output is the right choice for most cabins, especially for sensitive electronics, variable-speed motors, chargers, and modern appliances.
BigBattery’s 48V off-grid inverters include the APEX-6.5K, the EG4 6000XP, and the EG4 12000XP.
Build Charging Around Winter, Not Just Summer
Size panels for the lowest-production season, not the best summer day. A cabin using 6 kWh daily may need considerably more than 6 kWh of daily solar harvest, because inverter losses, charging losses, panel temperature, snow, and sun angle all reduce output.
For example, if your location averages 3 peak sun hours in winter and system losses total about 25%, a cabin using 6 kWh per day needs about 2.7kW of solar (6 ÷ 3 ÷ 0.75). A 3kW array is a sensible starting point. Check your own winter sun hours before you buy panels.
A generator paired with an appropriately sized battery charger is a practical backup during storms, maintenance, or high-load weekends. Batteries with open communication support compatible inverter-chargers for controlled charging and protection, so avoid proprietary ecosystems that limit your future choices.
Do Not Skip Cold-Weather Planning and Protection
Do not charge LiFePO4 batteries below freezing unless the battery has low-temperature charging protection or self-heating. Discharging in cold weather is less restricted, but available capacity still drops as temperatures fall. Check the battery’s low-temperature charging cutoff before you buy. Product documents lists specs and manuals for each model.
Install batteries in a protected, insulated, or conditioned space, or in a suitable sealed enclosure. Keep them away from weather, water, and heat sources, and leave room for service access. Use correctly sized fuses, breakers, and disconnects, and cable rated for the current and distance. Hire a qualified installer for service panels, generator integration, or high-current DC work.
Plan for the Cabin You Will Have Later
Many owners add internet, freezers, workshops, or cooling after the first season. Modular batteries and expandable inverters make that growth easier, provided the original design has room for it. For example, BigBattery lists the NEXUS 2 as expandable to 15 units, or about 241 kWh.
Before buying, check battery expandability, inverter parallel capacity, charge controller headroom, warranty terms, BMS protections, communication compatibility, and technical support. A low purchase price does not help if it locks you into one supplier or forces a full replacement later.
Get Help Sizing Your Off Grid Cabin Battery System
BigBattery’s Texas-based experts can turn your load list into a system plan, from a compact weekend retreat to a full-time off-grid property. Browse BigBattery’s off-grid battery systems, run your loads through the Solar Battery Sizing Calculator, or call (818) 280-3091.
Frequently Asked Questions
How big of a battery bank do I need for an off grid cabin?
Add up your daily energy use in kWh, multiply it by the days of storage you want, and divide by usable depth of discharge. A cabin using 6 kWh per day with two days of autonomy at 80% depth of discharge needs about 15 kWh of nominal capacity.
How many kWh does an off grid cabin use per day?
A small weekend cabin may use 2 to 4 kWh daily. A larger cabin with a full-size refrigerator, satellite internet, a washer, power tools, or a mini-split can reach 8 to 15 kWh per day. A plug-in power meter shows your real use.
Should an off grid cabin use 12V, 24V, or 48V?
12V suits a very small cabin with modest DC loads and an inverter under roughly 2,000 watts. 24V suits compact cabins with 2,000 to 4,000 watts of inverter power. 48V is the cleaner choice for full-time or expansion-minded cabins because it moves the same power with less current.
What size inverter does an off grid cabin need?
The continuous rating must cover the loads you run at the same time, and the surge rating must handle motor startups from pumps, compressors, and shop tools. Pure sine wave output is the right choice for most cabins.
How many solar panels do I need for an off grid cabin?
Size panels for your lowest-production season, not July. A cabin using 6 kWh per day may need considerably more than 6 kWh of daily solar harvest once inverter and charging losses, snow, and shade are counted. Your local peak sun hours decide the array size.
Do I need a generator for an off grid cabin?
Not always, but a generator is a sensible backup charging source during extended storms, maintenance, or high-load weekends. Pair it with an appropriately sized battery charger.
