How long does it take to charge a 100Ah battery with a 200W solar panel?

About 4 peak sun hours from half full, or 0.8 days at 5 sun hours a day. A 100 Ah, 12 volt battery going from 50% to full needs 600 Wh. A 200 watt panel at 75% system efficiency delivers 150 Wh per peak sun hour, and 600 / 150 = 4.

From empty, the battery needs 1,200 Wh, which is 8 peak sun hours or 1.6 days at 5 sun hours a day. Peak sun hours vary with location, season, weather and panel angle, so your days may be longer or shorter.

A lead-acid battery also slows down during its final topping stage, so the last part can lag behind the simple estimate. The solar charging time calculator takes your own sun hours, and the guide to solar battery charging covers losses and charge controllers.