What size battery do I need to run a 12V fridge?

To power a 12V fridge effectively, calculate the required battery capacity using this formula: Battery Capacity (Ah) = (Fridge Wattage × Runtime Hours) ÷ (12V × Efficiency Factor × Depth of Discharge). For example, a 60W fridge running 24 hours with 80% efficiency and 50% discharge depth requires ≈150Ah for lead-acid or ≈75Ah for lithium. Common 12V fridge batteries range from 50Ah (short trips) to 200Ah (multi-day use).

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How do I calculate runtime for a 12V fridge?

Runtime depends on fridge energy draw and battery capacity. Use a wattmeter to measure actual fridge consumption—typically 1–3Ah/hour. Multiply this by desired runtime hours and add 30% buffer for compressor surges and inefficiencies.

Start by determining your fridge’s average amp-hour draw per 24 hours. Most 12V compressor fridges consume 20–60Ah daily. If your battery bank is 100Ah with 50% usable capacity (lead-acid), you’d get 50Ah ÷ 2.5Ah/day = 20 hours runtime. Pro Tip: Lithium batteries (e.g., LiFePO4) provide 80% usable capacity, doubling effective runtime versus lead-acid. For example, a 12V fridge drawing 2Ah continuously would deplete a 100Ah lead-acid battery in 25 hours but last 40 hours with lithium. Always factor in ambient temperature—hot environments increase compressor workload by 15–30%.

What battery chemistry works best?

Lithium (LiFePO4) outperforms lead-acid for fridge applications due to higher cycle life, faster recharge, and stable voltage output. Lead-acid remains cost-effective for occasional use.

While AGM batteries handle moderate cycling (300–500 cycles), LiFePO4 provides 2,000–5,000 cycles with 80% depth of discharge. A 100Ah lithium battery delivers usable energy equivalent to a 200Ah lead-acid bank. Practically speaking, lithium’s flat discharge curve ensures your fridge’s compressor runs efficiently even as the battery depletes. Warning: Lead-acid voltages drop significantly below 50% charge, triggering premature low-voltage fridge shutdowns. For off-grid setups, lithium’s 90%+ round-trip efficiency (vs. 70–85% for AGM) maximizes solar recharge capability. Real-world example: A 12V 100Ah LiFePO4 battery running a 45L fridge can sustain 3–4 days of operation, whereas AGM lasts 1.5–2 days under identical conditions.

How does temperature affect battery sizing?

Cold reduces capacity while heat accelerates degradation. Lithium handles -20°C to 60°C better than lead-acid’s 0–40°C range.

Lead-acid batteries lose 30–40% capacity at 0°C, requiring oversizing in cold climates. Lithium retains 85% capacity at -20°C but needs heating pads below -10°C for charging. Conversely, in 35°C+ environments, lead-acid lifespan halves every 8–10°C above 25°C. Pro Tip: For desert RVers, choose lithium with built-in thermal management—their 10-year calendar life outperforms AGM’s 3–5 years in high heat. A 12V fridge in 40°C ambient might draw 25% more current, necessitating 25% larger battery capacity. Always install batteries in ventilated compartments to prevent thermal runaway risks.

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