By the way, those 26980 cells volchyonok posted look rather interesting: https://www.alibaba.com/product-detail/3-6V-26980-6000mAh-Lithium-Battery_60729304966.html

≈50% longer than 26650s, this certainly improves the surface to volume cell ratios. But they certainly need to be rather good cells to stand a chance against PLB 50A/55As. ¯\_(ツ)_/¯

Cheers :-)