Battery bank calculator
Daily usage, days of autonomy, depth of discharge, efficiency and voltage: you get nominal capacity in kWh and Ah and the number of modules.
Nominal capacity
6.94 kWh
- Nominal battery capacity6.94 kWh
- Capacity in amp-hours144.68 Ah
- Battery modules2 unit
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How it's calculated (visible formula)
kWh = daily use × days ÷ (DoD × efficiency); Ah = kWh × 1000 ÷ V
- Net geometric measurement, no waste.
- Adjustable waste % for cuts and breakage.
- Purchase rounded up to sellable units (boxes, bags, buckets, boards).
How to calculate it, step by step
- Work out the daily energy to cover from batteries.
- Choose days of autonomy.
- Enter depth of discharge for the chemistry.
- Apply round-trip efficiency.
- Get kWh and Ah at bank voltage and round up to modules.
Worked example: 5 kWh/day, 1 day, 80% DoD, 90% efficiency, 48 V
- 5 ÷ (0.8 × 0.9) = 6.94 kWh
- 6,940 ÷ 48 = 145 Ah
→ Two 5 kWh modules.
Common mistakes
- Discharging lead-acid below 50%.
- Ignoring inverter losses.
- Mixing batteries of different age or chemistry.
Pro tips
- For LFP lithium, 80–90% DoD is common and safe.
- Install in a ventilated space with moderate temperature.
- Don't mix batteries of different age, size or chemistry.
- Size the inverter for peak power, not just energy.
From calculation to quote
Add labour, overhead and your margin, and generate the professional PDF.
FAQs
- What depth of discharge?
- 80–90% for lithium (LFP); 50% for lead-acid.
- How many days of autonomy?
- 1 for grid-tied backup; 2–3 off-grid without a generator.
- 12, 24 or 48 V?
- 48 V above about 3 kW: lower current, thinner wire.
- How many batteries for a house?
- To cover 5 kWh overnight, about 7 kWh of lithium nominal capacity.
- How long do lithium batteries last?
- 4,000–6,000 cycles for LFP — over 10 years of daily use.
- 24 or 48 V?
- 48 V above about 3 kW.
Sources and standards
Maintained by Srikanta M · Formula v1.0.0 · Verified 2026-09-10 · Updated 2026-09-10 · Limits: quantity estimation, not structural design or site supervision.