My personal experience (disclaimer: your mileage may vary, batteries are not included, consumer to remove this sticker) has been that in multi-battery starting applications the weaker batteries inevitably drag the other ones down. Yes, same CCA *should* work fine, but I never had any luck with just removing dead batteries from a set and replacing with new "identical" batteries. The new ones bite the dust sooner when older batteries are in the mix.
The note to self is, if I have to replace one bad battery in a multi-battery application, I replace them all for THIS application and find new homes for the still serviceable batteries - either in single battery applications or in applications where I can combine just the "surviving" batteries without having to add any new ones.