You’re running into this ugly ‘equivalency’ business that sometimes plagues a type of product when the technology changes. Same as tires having ‘ply ratings’ which is not their actual ply count, or electric vehicles having ‘mpg-e’. Just clunky business we must navigate.
So the current that a bms will shut off over is time dependent. At some super high number it will trip almost instantly, at some lower current it will last 1-5 seconds, at some lower current than that it will sustain continuously it until the battery is drained.
So on principle i agree that a battery should not be rated using the ‘CCA’ rating unless it could hit the actual test conditions that that refers to, but technically a lifepo4 couldnt at all because i believe that test refers to the number of amps a battery can hit without dropping to 7.2 volts (the rest of the voltage being converted internally to heat due to the battery’s internal resistance), and a lifepo4 BMS would stop the test at ~10.0v.
So yeah, annoying but also something we must ‘deal with’ because better rating systems for lifepo4 as starter batteries have not been widely accepted. I can tell you that a lifepo4 will drop much less voltage internally and ‘act’ like a much bigger lead acid if you are comparing say 100ah to 100ah. For example, when i do a 100amp load test on a 100ah i am using as a starter battery, the voltage only sags to the region marked ~1100cca on the ‘cheat sheet’ of color coded regions on the analog voltage gauge of the tester. I have never seen an actual lead acid starter battery (up to group 94 or 31 size anyway) test that high on that little tool.
Any decently sized lifepo4 with a sufficiently large BMS (750a for 2 seconds is huge) will perform extremely well as a starter battery.
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