Battery Bank Calculator
Size your off-grid battery bank based on daily energy needs, system voltage, and desired days of autonomy.
Battery Type Comparison for Off-Grid Systems
Cost per usable kWh over battery lifetime
| Battery Type | DoD | Cycle Life | Cost per Ah (12V) | Usable kWh per $1,000 | Lifespan |
|---|---|---|---|---|---|
| LiFePO4 | 80-90% | 4,000-6,000 | $0.40-$0.60 | 1.5-2.0 kWh | 10-15 years |
| AGM Lead-Acid | 50% | 500-800 | $0.20-$0.35 | 0.7-1.0 kWh | 3-5 years |
| Flooded Lead-Acid | 50% | 800-1,200 | $0.12-$0.20 | 1.0-1.5 kWh | 3-7 years |
| Gel Lead-Acid | 50% | 500-700 | $0.25-$0.40 | 0.5-0.8 kWh | 3-5 years |
| Lithium NMC | 80% | 2,000-3,000 | $0.35-$0.55 | 1.2-1.6 kWh | 7-10 years |
How We Calculate This
This battery bank calculator uses established formulas and industry-standard data to provide accurate estimates.
- Enter your specific values into the calculator fields above
- Our algorithm applies the relevant formulas using your inputs
- Results are calculated instantly in your browser — nothing is sent to a server
- Review the detailed breakdown to understand how each factor affects your result
These calculations are estimates based on standard formulas. For critical decisions, always consult a qualified professional.
How to Convert Oven Recipes to Air Fryer
This calculator sizes an off-grid battery bank using the standard formula: Total Ah = (Daily Wh x Days of Autonomy) / (System Voltage x Depth of Discharge). It then calculates the number of batteries needed in series and parallel configurations.
The basic rule:
- Total energy needed = daily watt-hours x days of autonomy
- Required Ah at system voltage = total energy / system voltage / depth of discharge (DoD)
- DoD varies by battery type: LiFePO4 = 80-90%, AGM = 50%, Flooded = 50%, Gel = 50%
- Series strings raise voltage (e.g., two 12V in series = 24V); parallel strings add capacity
- Total batteries = series batteries per string x parallel strings needed
LiFePO4 batteries cost more upfront but last 3-5x longer than lead-acid (4,000+ cycles vs 500-800 cycles), making them cheaper per kWh over their lifetime. Always include a charge controller and fusing appropriate for your battery bank configuration.
When Would You Use This Calculator?
This battery bank calculator is designed for anyone who needs quick, reliable estimates without complex spreadsheets or professional consultations.
- When you need a quick estimate before committing to a purchase or project
- When comparing different options or scenarios side by side
- When planning a budget and need to understand potential costs
- When you want to verify a quote or estimate you've received from a professional
- When teaching or learning about the concepts behind these calculations
Frequently Asked Questions
What are days of autonomy?
Days of autonomy is how many days your battery bank can power your loads without any recharging (no sun, no generator). In sunny climates, 2-3 days is typical. Cloudy regions or winter use may need 4-5 days. More autonomy means a larger, more expensive battery bank but better reliability.
What depth of discharge should I use?
LiFePO4 batteries can safely discharge to 80-90% DoD regularly. Lead-acid batteries (AGM, flooded, gel) should only be discharged to 50% to preserve lifespan. Discharging lead-acid below 50% dramatically shortens battery life — from 800 cycles to under 200 cycles at 80% DoD.
Should I choose 12V, 24V, or 48V?
12V systems work for small loads under 2,000W (RVs, boats, small cabins). 24V systems suit mid-size off-grid cabins (2,000-5,000W). 48V is best for larger homes (5,000W+). Higher voltage means lower amperage for the same power, allowing smaller wire sizes and less energy loss over distance.
How long do off-grid batteries last?
LiFePO4 batteries last 10-15 years (4,000-6,000 cycles). Quality AGM batteries last 3-5 years (500-800 cycles). Flooded lead-acid batteries last 3-7 years with proper maintenance (800-1,200 cycles). Temperature, depth of discharge, and charging practices all affect lifespan.
What size solar array do I need to charge this battery bank?
A general rule is your solar array should produce 1.2-1.5x your daily watt-hour consumption to account for system losses and partial sun days. For a 3,000 Wh/day system, you need 3,600-4,500W of solar production, which in a 5 peak-sun-hour area means 720-900W of panels.
LiFePO4 vs lead-acid for off-grid — which is better?
LiFePO4 wins on almost every metric except upfront cost. Benefits include 80-90% usable capacity (vs 50% for lead-acid), 4,000+ cycle life, no maintenance, lighter weight, and flat discharge curve. A 200Ah LiFePO4 battery provides as much usable energy as a 400Ah lead-acid battery at half the weight.