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Battery Size Calculator

Size your home backup or off-grid solar battery bank in Kilowatt-Hours (kWh) and Amp-Hours (Ah) for reliable energy autonomy.

Calculator Inputs

Live
kWh
1 kWh30 kWh
%
30%90%
Calculation Results
Battery Storage Capacity
7.5 kWh
Equivalent to 156.3 Ah at 48V DC
100Ah Batteries Needed
2 units
200Ah Batteries Needed
1 units
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How to use the Battery Size Calculator

  1. 1Enter your daily backup energy requirement in kWh (e.g. 5 to 15 kWh).
  2. 2Enter desired days of autonomy (number of days the battery can run without grid or solar power).
  3. 3Select battery Depth of Discharge (DoD) percentage (80% for Lithium, 50% for Lead-Acid).
  4. 4Select DC system voltage (12V, 24V, or 48V).
  5. 5View total battery storage needed and recommended 100Ah/200Ah battery counts.

How Battery Size is Calculated

Total daily kWh is multiplied by days of autonomy and divided by the Depth of Discharge (DoD) limit. Dividing total energy by system DC voltage yields Amp-Hours (Ah).

Mathematical Formula
Battery Capacity (kWh) = (Daily kWh × Days of Autonomy) / (DoD % / 100) Battery Capacity (Ah) = (Battery Capacity (kWh) × 1,000) / System Voltage
Formula Variables & Logic

Lithium iron phosphate (LiFePO4) batteries safely support 80-90% DoD, while tubular lead-acid batteries should not exceed 50% DoD.

Worked Example: Home Power Backup System
Sample Calculation
Scenario: Requiring 4 kWh of daily backup for 1 day of autonomy using 48V Lithium-ion batteries (80% DoD).
Step-by-step breakdown
  1. 1Storage Needed = (4 × 1) / 0.80 = 5.0 kWh
  2. 2Capacity in Ah = (5.0 × 1,000) / 48V = 104.2 Ah at 48V
Estimated Result
A 5.0 kWh battery bank (approx 105 Ah at 48V) is recommended.

What affects Battery Size results

  • Battery chemistry (Lithium LiFePO4 vs Gel vs Flooded Lead-Acid).
  • Ambient temperature (freezing temperatures diminish usable capacity).
  • High discharge current rates accelerating degradation.
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Frequently Asked Questions

What is Depth of Discharge (DoD)?

Depth of Discharge (DoD) is the percentage of a battery capacity that has been discharged relative to its overall capacity. Discharging deeper than recommended shortens battery cycle life.

Why is a 48V battery bank preferred over 12V for solar systems?

Higher system voltage reduces electrical current for the same power, allowing thinner copper cables, lowering resistive losses, and improving inverter efficiency.

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