Just read the second part of theis pair of articles. Quite disappointing. No mention of any workshop projects or what cells / batteries are suied to what. In fact there are a few clues that indicate this has been re-purposed from an astronomy publication. Mention of cooled camers, dew heaters and astronomical equipment.
It mentions using step-up converters with secondary lithium cells, specifically cheap modules based on the MT3608. While it covers the fact the the 2A output current is optimistic for a single cell input even the example of 1A at 12V is not possible within the ratings of the device. The datasheet indicates 0.8A max for 5V in 12V out. For a 4V input you would be limited to 700mA output even without consideration of how much current the cell can provide. Practically I would not go above 500mA. They also say that the device is not usable for a 12V input. This is not correct, they can operate up to 24V in 28V out (depending on the voltage rating of the capacitors used).
Finally there are no real warnings about the dangers of lithium cells, particuarly re-purposed ones, or fire precautions to be taken when charging them.
Another thing that is often missed is that “homemade” rechargable lithium batteries ar considered hazardous materials and cannot be posted, shipped or carried on aircraft (even in carry on).

Robert.