To cut boards and other things in straight lines, a circular saw is just the thing. The saw has a voltage of 12 volts and weighs 2.2 kg, so it's not that heavy to carry around.
From ManoMano
DCS512N 12V xr Cordless Brushless 140mm Circular Saw Bare Unit - Dewalt
This product is also available at 4 unverified stores.