I bought your 100ah starting battery but it's too big IMO. I would gladly sacrifice some AH for something smaller (say group 24 size). Also if there was a way to limit charge amperage (so I didnt need a DCDC charger) that would be good to calm my fears of frying alternators on older motors.
Your question is about how to make parallel discharge work as one would expect it to work. But does anyone know what the manufacturer was trying to accomplish with this strange behaviour that prevents discharge when in parallel?
Edit> it appears that I've posted this comment to the wrong thread. 😝
@Rascally I was gonna say, I'm new to Lifpo4 but not that new......your answer made me think I was in over my head!
@KevenLikeSeven lol. About your question... if your lithium battery is charged by your alternator, you'll need to protect the alternator from two things, 1) overheating due to tremendously low impedance of the LFP battery, and 2) from burning out the alternator's diodes if the battery's BMS decides to shutdown, as it will do when it reaches its set limit for high voltage shutdown.
A lithium battery mustn't be connected directly to a standard alternator, one with internal regulation. An externally regulated alternator can be setup correctly, with the external regulator communicating necessary information to the alternator.
@KevenLikeSeven, also... is this lithium battery is your starter battery? If so, you'll probably kill the battery. It may not be big enough.
Have you verified the load required to start your engine? I don't know what engine you're starting, but I'm surprised you have a 100AH Start Battery.
Lead Acid are superb Start batteries. It's difficult to imagine a scenario where LFP is preferred.
I bought this one. It won't be my primary starting battery but I wanted it to have start capabilities in case of emergency:
https://www.wattcycle.com/products/wattcycle-12v-100ah-1200cca-marine-cranking-battery-with-bluetooth?srsltid=AfmBOoq9k8Wj3W9VhRGCB_F8CGuB1J9ebYRKK4ymkTSVu6FNFc2WsPUr
@KevenLikeSeven, as a spare Start battery, it'll probably work, but it would be wise to compare the loads pulled by the starter vs the battery's CCA. Used regularly for Start, I'm sure that LFP would have a short life.
also, be aware that having an LFP kept at full charge will also degrade the battery life. Unlike lead acid batteries, LFP's degrade quicker when spending time at full charge. Another plus for lead acid used for Start.
