> any lithium battery from a drill to a tesla is simply a 1.5 volt cylindrical cell Incorrect. Lithium Ion batteries are 3.7V (nominal) with different chemistr

> any lithium battery from a drill to a tesla is simply a 1.5 volt cylindrical cell Incorrect. Lithium Ion batteries are 3.7V (nominal) with different chemistries varying from 3.2V (LiFePO4) to 3.8V (LiHV). >The safety features you're so worried about are just fuses. And maybe some diodes if you're that worried. Also incorrect. It won't just have fuses, but also low voltage (over-discharge) protection, high voltage (over-charge) protection, and transient current limiting with auto reset, typically done with an IC + FETs per small pack of cells or even per cell. So before you can build your pack you need to make sure that the cells all have the same chemistry and charge level, and that the ICs are programmed to cut out at the same voltage and current, otherwise you get nasty surprises when connecting in parallel (the voltage mismatch) or in series (current mismatch) or any hybrid of the two. Source: specced and sourced cells, safety ICs and chargers for portable payment terminals. And 15 years experience in electric RC aircraft.