I'm planning on following the recommendation of an Australian YouTuber who suggests the best chance of the longest Apple laptop battery life is to keep the charge between 50 & 80% of the maximum.
Earlier in the week I bought a 13,500 mAh (output) battery capable of charging at 45W via PD/USB-C. My M1 MacBook Air's charger supplies 30W. The battery has a separate USB-A port rated at up to 18W although if used in conjunction with the 45W USB-C port the output drops from 18W to 10W. The USB-A port has a low-power mode for circuits requiring less than 200 mA. This will make it easy to maintain the M1 MacBook Air within the 58-80% range by freeing me from the need to charge via mains power.