To effectively charge a 120Ah battery, you typically need around 300W of solar panels. Use one 300W panel, two 150W panels, or three 100W panels. Ensure your configuration fits your RV space. Also, consider charging times and usage scenarios to optimize efficiency and performance. Now, multiply the. Choosing the correct size solar panel to charge a 12V battery is crucial for maintaining an efficient and reliable solar power system. Enter battery capacity in amp-hours (Ah): I have already put 120ah for you. Select battery type: Is this a. Enter your 12V loads, panel size, and battery — get panels needed, charge controller size, and battery autonomy instantly. 100W panels for vans and boats. You need a reliable way to keep your battery charged, but how do you choose the right solar panel? This article will guide you through the process. In this article, we'll guide you through the key factors to consider when sizing a solar panel for a 120Ah battery, including important calculations, different battery types, and practical recommendations for optimal performance.