Recently, the demand for electric tractors has grown substantially in efforts to achieve carbon neutrality. To successfully introduce electric tractors into the market, ensuring sufficient working duration on a single charge is crucial. Increasing the battery capacity is one approach to extend the working duration. However, structural weight reduction strategies for tractors should be explored to mitigate potential issues associated with excessive weight, such as soil compaction. To increase the working duration of electric tractors, this paper proposes methods for structural weight reduction, to predict working duration per agricultural work based on tractor weight reduction, and to predict the appropriate battery weight for electric tractors. The proposed method involves implementing topology optimization on the rear axle housing of tractors to achieve weight reduction. The allocation of weight reduction resulting from structural improvements to the battery weight is determined using a dynamic model of a tractor to calculate the increase in working duration. Additionally, the extended working duration for various agricultural works is estimated, considering different types of batteries and battery weight ratios. Notably, light-weighting achieved a 20.21% reduction in weight when compared with the initial model. The findings of this study indicate an increase in the working duration, with approximately 56.2 and 7.1 min additional for road driving and rotavator work when using Li-S batteries, respectively. Furthermore, the battery weight required to achieve the targeted working duration is calculated, accounting for variations in power demand across different agricultural works. Finally, a method for predicting the optimal battery weight for electric tractors based on the specific power needs and targeted working duration for various agricultural activities is proposed.