How long will a 100Ah lithium battery run a 12V fridge?

A 100Ah lithium battery typically powers a 12V fridge for 40–60 hours, depending on fridge efficiency (1.5–3A draw), ambient temperature, and battery discharge depth. LiFePO4 batteries allow 95% usable capacity (95Ah vs. 50Ah in lead-acid), extending runtime. Example: A 12V fridge drawing 2A/hour runs ~47.5 hours on a single charge. Always derate capacity by 10% for inverter/controller losses.

Best RV Battery for Solar Power Systems

How does fridge amp draw affect runtime?

Fridge current consumption directly dictates battery life. High-efficiency 12V fridges (e.g., Dometic CFX3) use 0.8–1.2A/hour in eco mode, while older models may pull 3–4A. Pro Tip: Multiply fridge amps by 24 to estimate daily Ah needs—e.g., 2A × 24h = 48Ah/day.

Deep Dive: Modern compressor fridges cycle on/off, reducing average draw. For a 2.5A fridge running 50% duty cycle (1.25A average), a 100Ah LiFePO4 battery provides 95Ah ÷ 1.25A = 76 hours. However, real-world factors like ambient heat or frequent door openings can slash this by 30–50%. Analogous to fuel efficiency in cars—aggressive driving (high temps) burns through “battery fuel” faster. Always check the fridge’s spec sheet for “AH/day at 25°C/40°C” ratings.

What’s the role of ambient temperature?

Ambient heat forces fridges to work harder, increasing compressor runtime by up to 70%. A 12V fridge consuming 1.8A at 20°C might draw 3.1A in 35°C desert conditions.

Deep Dive: Thermodynamics dictate that every 5°C above 25°C raises compressor workload by ~25%. For example, a 100Ah battery powering a 2A fridge at 25°C lasts 47.5 hours, but only 28 hours at 40°C. Think of it like running a marathon uphill versus on flat ground—the same effort yields shorter distances. Pro Tip: Use insulated fridge covers and park vehicles in shade to reduce thermal load.

How does battery chemistry impact performance?

LiFePO4 batteries outperform AGM/gel in depth of discharge (DoD) and cycle life. While lead-acid degrades beyond 50% DoD, lithium handles 80–100% daily.

Deep Dive: A 100Ah AGM battery only provides 50Ah usable (50% DoD), whereas lithium offers 95Ah. For a fridge needing 48Ah/day, AGM lasts ~1 day vs. lithium’s 2 days. It’s like comparing a 10L fuel tank (AGM) to a 19L tank (LiFePO4). Plus, lithium maintains stable voltage under load—no “voltage sag” reducing fridge efficiency. Pro Tip: For RVers, lithium’s 3,000–5,000 cycles (vs. 500 in AGM) justify the higher upfront cost.

Can solar panels extend runtime indefinitely?

With proper solar replenishment, yes. A 200W solar panel generates ~60Ah/day (sunny climate), offsetting a 48Ah/day fridge draw.

Deep Dive: Solar extends battery life by countering daily depletion. For a 100Ah battery and 200W panel: 60Ah solar input – 48Ah fridge output = +12Ah/day surplus. Overcast days complicate this—50% cloud cover cuts solar yield to ~30Ah. Think of it as a leaky bucket: solar pours water in while the fridge drains it. Balance both flows for indefinite runtime.

What inverter losses occur with AC fridges?

Inverters waste 10–15% energy converting DC to AC. Running a 120V fridge via a 12V inverter reduces effective battery capacity by 25% versus native 12V models.

Deep Dive: A 100Ah battery holds 1,280Wh (12.8V × 100Ah). A 120V AC fridge drawing 1.5A (180W) would run for 1,280Wh ÷ (180W ÷ 0.85 inverter efficiency) = ~6.3 hours. Compare this to a 12V DC fridge using 15A (180W): 1,280Wh ÷ 180W = 7.1 hours. Why the gap? Inverters idle at 10–20W even when unused. Pro Tip: Use DC fridges whenever possible—they’re 30% more energy-efficient.

Fasta Power Expert Insight

FAQs