Battery Backup Calculator
Calculate battery backup size for load shedding. Compare LiFePO4, gel, and lead acid costs. Battery vs generator 5-year cost comparison.
Quick Calculator Get a fast estimate
W
hours
Battery Bank Size
4 kWh
Estimated Cost
R 26 000
Expected Lifespan
11 years
Daily Cycles at Stage ${stage}
1 cycle/day
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Battery Backup Formula
Battery size (kWh) = Load (W) × Hours ÷ 1000 ÷ Depth of Discharge. LiFePO4 batteries allow 80% DoD, meaning an 800W load for 4 hours needs: 800 × 4 ÷ 1000 ÷ 0.8 = 4 kWh. At R6,500/kWh installed, this costs approximately R26,000 for batteries alone.
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Extended Calculator More options, charts, and scenario comparison
hours
Select Appliances to Power
Total Load
555W — 2,22 kWh for 4h
LiFePO4 Lithium
2,8 kWh = R 18 038
Gel / AGM
3,7 kWh = R 11 100
Lead Acid
4,4 kWh = R 8 880
Battery Chemistry Comparison
| Type | DoD | Cycles | Cost/kWh | Lifespan |
|---|---|---|---|---|
| LiFePO4 Lithium | 80% | 4,000+ | R 6,500 | 10–12 years |
| Gel / AGM | 60% | 600 | R 3,000 | 2–3 years (daily) |
| Lead Acid (flooded) | 50% | 400 | R 2,000 | 1–2 years (daily) |
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Professional Calculator Complete parameters, sensitivity analysis, and detailed breakdown
Battery vs Generator Analysis
W
h
W
Battery System
4,1 kWh — R 34 304
Battery
R 26 804
Inverter
R 7 500
Life
11 yrs
Battery vs Generator — 5-Year Comparison
| Cost Component | Battery | Generator |
|---|---|---|
| Capital Cost | R 34 304 | R 2 800 |
| Fuel/Running (annual) | R 0 | R 9 072 |
| Depreciation (annual) | R 3 130 | R 560 |
| 5-Year Total | R 49 955 | R 50 960 |
Generator fuel: 34L/month at R22.50/L. Generator size: 0,8 kW.
Battery Type Comparison
| Type | DoD | Cycles | Cost/kWh | Best For |
|---|---|---|---|---|
| LiFePO4 | 80% | 4,000 | R6,500 | Daily cycling |
| Gel/AGM | 60% | 600 | R3,000 | Occasional use |
| Lead Acid | 50% | 400 | R2,000 | Budget backup |
Note: Prices are 2024 South African market estimates. LiFePO4 lithium batteries have become the preferred choice for daily load shedding cycling due to longer lifespan and no maintenance. Lead acid still offers the lowest upfront cost for occasional use.
Frequently Asked Questions
Your inverter must handle your peak load. For 800W continuous load, a 1.5–2 kVA inverter is sufficient. Add surge capacity for fridges (3–5× starting watts) and motors. A 3 kVA inverter handles most home essentials including a fridge, lights, TV, and laptop charging simultaneously.
Battery inverters win on convenience (instant switchover, no noise, no fumes, no fuel runs) and long-term cost. Generators win on upfront cost and unlimited runtime. For Stage 2–4 load shedding, a 5 kWh battery system typically pays back its premium over a generator within 3–4 years due to fuel savings.