I can’t use a calcium battery in my older car because my alternator has a lower output charge rate.

This is not true.  Calcium in the positive and negative plates makes the battery more resilient and allows it to have a higher output. The calcium raises internal resistance and is suited to higher charge rates.

 

Calcium batteries have a higher output and can be used in all vehicles. Use a suitable charger to maintain the battery if it’s flat or not used often.