Circular saws are well-tested and efficient tools when it comes to cutting things. The voltage amounts to 18 volts and weighs 2.9 kg, so it's not that heavy to carry around.
From Amazon
Bosch Cordless Circular Saw UniversalCirc 18V-53 (Precise Sawing in Wood; Max Cutting Depth 53 mm; 18 Volt System; Without Battery)
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