dual battery set-up

I'm putting in a dual battery set-up in and have a question. I have the Tsunami X151700 battery and I will be putting in 2 Tsunami X15925 batteries in parralel and seperated by a 200 amp relay from the X151700.

I hear some people say it's not good to run different batteries because of internal resistance differences, it's harder on the alternator. these batteries are from the same "family" of batteries and the resistance isn't too different. should I not worry about it and see what happens? I already have the batteries so returning them is out. any thoughts?

Because you're using the relay I don't see where this would be a problem..  I'm assuming that the relay would disconnect the dual batteries when the engine is off, and all batteries would only be connected together when the engine is running.

It would be good to have the two X15925 from the same batch.. but with the relay disconnecting the duals from the engine start battery when the engine is off you shouldn't see any problems.

Jim