Home Backup Battery Size Calculator

Battery Capacity Formula:

\[ \text{Battery Capacity (Ah)} = \frac{\text{Daily Energy Usage (Wh)} \times \text{Days of Autonomy}}{\text{Battery Voltage (V)} \times \text{Depth of Discharge} \times \text{Efficiency}} \]

Daily Energy Usage:

Days of Autonomy:

days

Battery Voltage:

Depth of Discharge:

(0-1)

Efficiency:

(0-1)

Required Battery Capacity:

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1. What is Battery Capacity Calculation?

The battery capacity calculation determines the required size of a backup battery system based on your daily energy consumption, desired backup duration, and system characteristics. It ensures you have enough stored energy to meet your needs during power outages.

2. How Does the Calculator Work?

The calculator uses the following formula:

\[ \text{Battery Capacity (Ah)} = \frac{\text{Daily Energy Usage (Wh)} \times \text{Days of Autonomy}}{\text{Battery Voltage (V)} \times \text{Depth of Discharge} \times \text{Efficiency}} \]

Where:

Daily Energy Usage — Your daily power consumption in watt-hours
Days of Autonomy — Number of days you want backup power
Battery Voltage — System voltage (typically 12V, 24V, or 48V)
Depth of Discharge — Maximum percentage of battery capacity you can use (0.5 for lead-acid, 0.8 for lithium)
Efficiency — Battery system efficiency factor (typically 0.85-0.95)

Explanation: The equation calculates the amp-hour capacity needed to store sufficient energy for your requirements while accounting for system losses and battery limitations.

3. Importance of Proper Battery Sizing

Details: Correct battery sizing prevents over-discharge (which damages batteries) while ensuring adequate backup power. Undersized systems fail when needed, while oversized systems are unnecessarily expensive.

4. Using the Calculator

Tips:

Measure your actual daily energy usage for accurate results
For lead-acid batteries, use DoD of 0.5 to extend battery life
For lithium batteries, DoD can be 0.8 or higher
Typical efficiency values: 0.85 for lead-acid, 0.95 for lithium

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between Wh and Ah?
A: Watt-hours (Wh) measure energy, amp-hours (Ah) measure charge. They're related by voltage: Wh = Ah × V.

Q2: How do I determine my daily energy usage?
A: Check your electricity bill for kWh usage, then divide by 30 and multiply by 1000 to get average daily Wh.

Q3: What's a typical DoD for different battery types?
A: Lead-acid: 50%, Lithium-ion: 80%, LFP: 90%. Higher DoD reduces battery lifespan.

Q4: Why include efficiency in the calculation?
A: Efficiency accounts for energy losses in charging/discharging, inverter losses, and other system inefficiencies.

Q5: How does temperature affect battery capacity?
A: Cold temperatures reduce available capacity (up to 50% at freezing). Consider temperature compensation for outdoor installations.