Guide to Calculating Battery Runtime for Optimal Performance

We've all experienced that frustrating moment when a crucial device suddenly warns of low battery - whether during an important work session, while watching a live sports event, or in other critical situations. Understanding how to accurately calculate battery runtime can help eliminate this power anxiety.

Specialized battery runtime calculators can provide quick estimates by considering multiple factors. One such tool accounts for:

• Inverter efficiency (90%)
• Battery discharge efficiency (85% for lead-acid, 95% for lithium batteries)

• Inverter efficiency: 90%
• Battery discharge efficiency: 85% for lead-acid, 95% for lithium

Note that these calculators don't account for Peukert's Law (which explains how battery capacity decreases with higher discharge rates) or temperature effects.

The calculator requires these inputs:

• Battery capacity (Ah): Convert Wh to Ah by dividing by battery voltage
• Battery voltage (V): Typically 12V, 24V, or 48V
• Battery type: Lead-acid or lithium
• State of Charge (SoC): Current charge percentage (100% when full)
• Depth of Discharge (DoD) limit: Manufacturer's recommended maximum discharge percentage
• Inverter connection: Whether load connects through inverter
• Total load (Watts): Combined power draw of all connected devices

Formula: Battery capacity (Ah) ÷ Output current (A)
or: Battery capacity (Wh) ÷ Total output power (W)

Example: A 50Ah battery powering a 10A load:
50Ah ÷ 10A = 5 hours runtime

Formula: (Battery capacity × Voltage × Discharge efficiency × DoD × SoC × Inverter efficiency) ÷ Load power

Example: 50Ah 12V lead-acid battery (85% efficiency, 50% DoD, 100% SoC) with 90% inverter efficiency powering 120W load:
(50 × 12 × 0.85 × 0.5 × 1 × 0.9) ÷ 120 = 1.9 hours

Battery capacity decreases at higher discharge rates. Lead-acid batteries show more significant capacity loss than lithium batteries under heavy loads.

Capacity diminishes with charge cycles. Lead-acid batteries typically last 500 cycles (losing 20% capacity), while lithium batteries can endure 2000 cycles before similar degradation.

Performance drops about 50% when operating outside the ideal 20-25°C range.

70Ah Lead-acid Battery:

200Ah Battery Comparison:

Battery runtime calculation involves numerous variables including battery type, capacity, load, temperature, and age. While calculators and formulas provide estimates, understanding their limitations helps make more accurate predictions. This knowledge empowers users to better manage their power needs and avoid unexpected disruptions.