SettingsSettings for this calculationUS
Energy used per day.
From a bill, divided by the days it covers. For a backup system, count only the circuits you intend to keep running — sizing to whole-house consumption when you plan to back up a fridge and some lights is how batteries get bought at three times the needed size.
Days the bank must run with no charging.
One day for grid-tied backup. Two to three for off-grid in a sunny climate; four or more where winter cloud is persistent. Each extra day is a linear cost increase and the largest single driver of the bill.
Chemistry sets how much of the nameplate you can actually use.
Depth of discharge is the big one. A lead-acid bank discharged past 50% loses cycle life rapidly, so half its nameplate is unavailable in practice — which is why a lithium bank of half the rated size can deliver the same usable energy.
Nameplate capacity required
11.7 kWh nameplate
Nameplate needed to deliver the stated usable energy. Real capacity falls with age and with temperature — a bank at 0 °C (32 °F) delivers materially less than its rating.
- Energy required at the load
- 10 kWh
- Usable share of nameplate
- 85.5 %
- Depth of discharge
- 90 %
- Round-trip efficiency
- 95 %
- At 48 V nominal
- 243.66 Ah
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Battery Bank Sizing Calculator: 11.7 kWh nameplate — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Usable capacity = nameplate × depth of discharge × round-trip efficiency. Lithium iron phosphate DoD 80-100%; lead-acid 50% to preserve cycle life
- Round-trip efficiency: LiFePO₄ 90-95%; flooded lead-acid 75-85% — manufacturer datasheets
Inputs used
- Daily load (kWh)
- 10
- Days of autonomy
- 1
- Battery chemistry
- LiFePO₄ — 90% DoD, 95% round-trip
Intermediate steps
- Energy required at the load
- 10 kWh
- Usable share of nameplate
- 85.5 %
- Depth of discharge
- 90 %
- Round-trip efficiency
- 95 %
- At 48 V nominal
- 243.66 Ah
Confidence note: Nameplate needed to deliver the stated usable energy. Real capacity falls with age and with temperature — a bank at 0 °C (32 °F) delivers materially less than its rating.
What this calculation does not cover
- Capacity fades over life. Most warranties guarantee 70-80% of nameplate at end of term, so a bank sized exactly today is undersized in year eight.
- Cold reduces available capacity substantially, and lithium cannot be charged below freezing without a heater.
- Says nothing about power. A bank with enough energy can still be unable to start a motor — that is a continuous and surge kW question, not a kWh one.
Add the equipment this sizes
This result is a specification — 11.7 kWh nameplate — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-08-27 · in the site-wide review of 2026-09-06 · v1.0.0
Regulatory standards & verification citations2
- Usable capacity = nameplate × depth of discharge × round-trip efficiency. Lithium iron phosphate DoD 80-100%; lead-acid 50% to preserve cycle life
- Round-trip efficiency: LiFePO₄ 90-95%; flooded lead-acid 75-85% — manufacturer datasheets
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