The time it takes to charge a solar battery depends on a few factors such as the size of the battery, the power of the solar panel, and the amount of sunlight. However, typically, a solar battery can be fully charged from 5 to 12 hours under optimum conditions. Formula: Charging Time (h) ≈ (Battery Ah × V × (Target SOC / 100)) ÷ (Panel W × (Eff% / 100)). Adjust for sunlight hours to find daily charging duration. In less than ideal conditions, this. But it brings up a big, practical question: how long does it actually take to charge the thing from your solar panels? The short answer is usually around 5 to 10 hours, but the real answer depends on a whole lot more than just the clock.