There is a way from Battambang to Tatai via Treng-Samlout-Vealveng. It is a very scenic road, with relatively decent quality asphalt on its first half until crossing Road 55. After crossing Road 55, the second part is tarmac and somewhat adventurous even during the dry season.
However, some parts of the road might not be usable during the rainy season. So please check the weather conditions before travelling and do not attempt this journey alone during the rainy season.