38120 or 18650 vs pre made battery back

I'm upgrading the electric system on my sailboat in the next few months in anticipation of putting lifepo4.

I'm kind of at a point of deciding if it would be smarter to build my own from 38120 or 18650 cells for example , or simply buying a complete battery from somewhere like AliExpress eg 100 or 200AH 12V packs. The pricing seems similar.

My concern with the last approach if what happens if I lose 1 or two cells in the sealed battery package.. presumably the whole battery is gone. And with a 1 year only warranty from a distant China that's going to be a bit tough. I assume if I make this from cells I can always go pack and replace defective cells.

But how likely is that? Does anyone have any real life data on the the likelihood of early life failure in these complete battery backs..?

If you're buying new, go with LiFePO4 cells, since they are compatible with 12V based systems.

And, most people are using cell level fuses so if a cell goes bad, it doesn't bring the whole system down. However, if they are new, there isn't really a need for cell level fusing as you know the condition of them. You could do bank level, where there's a group of parallel that are fused to the larger pack. Example of an 80p pack, and fuse groups of 10p. Mike has started doing this, and I believe HBPowerwalls has started doing this as well.