Automotive starting circuit capacity

Many of the batteries I have been looking at, such as the SOK, have a maximum 100 Amp @ 12V discharge rate. However, an automotive diesel starter motor can draw up to 650 Amps for a short duration. I am concerned that if I apply an SOK to this use case, it will not be adequate to start my truck.

Also, will the battery management system cut the circuit if it exceeds 100 Amps, or do I potentially damage the battery? I ask, because my truck has two batteries, perhaps one battery could be a lithium back-up and the lead-acid the primary starting battery.

Automotive start batteries, and lead-acid batteries designed for off-grid use, are very different for each other and are not good replacments for each other. Automotive batteries are designed with very thin lead plates that can give a very high current discharge for a short period of time. Then they must be recharged almost immediately. Off-grid batteries have much thicker plates that produce less current, but can continue producing that lower current for many hours before a recharge cycle is completed. Try to replace one for the other and you will get poor performance and short-lived batteries.

For your application, it would be best to keep two different battery banks completely separate from each other, one for starting, and one for powering stuff.

Thanks Michael,
I appreciate your detailed response. You are confirming what I suspected. Will P. has a diagram for alternator assisted solar charging using a Renology controller, that provides charge management of two separate banks. You have confirmed that I will still rely on lead-acid for the main truck batteries.

On 100a lithium batteries they can usually do 100a continuous, and 200a peek. After a short time at 200a bms cuts out.

Starting batteries for starting.
Deep cycle for running stuff.
And dual purpose in the middle.

AGM batteries can fall in that dual purpose catagory and could be deep cycled, or start. But you don't want to kill your starting batteries and leave yourself stuck.

You also don't want to mix battery types when they are in the same bank.

It might be possible to get put some AGMs in, separate the batteries. One for starting, one for house. Then put a paralleling switch in- a relay that connects and disconnects the two. 1 battery may not be enough to start the truck. But 1 full battery linked to one not so full battery might start it.

The better option is probably to leave the starting batteries, get a lithium, and the charger from renogy.

There's a few ways to separate out a battery bank, isolater relay, isolater diode, or charger. I haven't kept up with the newer stuff, but the charger reviewed is probably best.