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Nick Dawbarn

While I completely agree with your main point, there is one major difference in that lithium batteries have some *very* impressive current delivery characteristics. This means that substandard systems that maybe you could have just got away without major incident suddenly become pretty spectacular failures when a few hundred amps are getting dumped through them (which of course shouldn’t happen with a proper BMS, which is again back to your main point…).
Like so many other things in sailing (and life) more power indiscriminately applied seldom produces desirable results.

Garryck Osborne

Which, again, comes down to “poorly designed and installed electrical systems”, and not the batteries themselves.

Nick Dawbarn

Yeah I think we all agree that the batteries are not at fault here 🙂

I’m just trying to make a subtle point that design has to take into consideration all the parameters of the system, and that lithium batteries have some very surprising design parameters for anyone coming over from older battery chemistries. A 50+C discharge rate is a completely nuts amount of instantaneous power, but not remotely unusual in a lithium system. With those design parameters achieving a properly designed system can take a bit of work!

It’s one reason why I find the practice of selling “drop-in” lithium systems so dangerous. You can’t change one of the fundamental design parameters without then going and reviewing the design of the system as a whole. The definition of the “poorly designed” part can change when you start messing with things. I can imagine a design that I’d consider “just adequate” with a small AGM system moving to “disaster waiting to happen” when you put a couple of “drop in” lithiums behind it.

Olivier Le Carbonnier

what do you think of a mixed lifepo4 Pb assembly like the one recommended here ?

Matt Marsh

Don’t put lead-acid in parallel with LFP.
You can, where necessary, use a DC-to-DC charger to connect both a sensitive load, and a dedicated small AGM or gel-cell battery for that load, to the main lithium-powered bus. This is essentially the same as a “Full Conversion UPS” in computer land, and prevents any brownouts/blackouts to that specific device, at the cost of extra weight, complexity, and dollars.