Estimate how long solar charging actually takes — using real-world panel output, not the optimistic rated wattage on the box.
Methodology: charge time = remaining Wh needed ÷ (panel's rated watts × a real-world derating factor). The derating factor accounts for panel angle, temperature, and the fact that manufacturer wattage ratings are measured under lab-ideal test conditions rarely seen outdoors. This is a general estimate, not a per-product verified figure — always cross-check against the manufacturer's own charge-time spec when available.