Isn’t a Dedicated Starting Battery Inefficient Use of a Battery?

Question:

I have a (5) 95Ah AGM house batteries and (1) 95Ah AGM starter battery (all same chemistry). Having a good battery that is used to draw just a few amps after starting and then sits idle seems to be a very inefficient use of a battery?  What are your thoughts please on combining all (6) batteries into one bank that is used for house and starting duties?  

A low cost 70Ah (Volvo D 2-55 engine) deep cycle emergency battery ( $150?) that can be connected with jumper leads to the starter motor and likely never used would be trickle charged from the main battery bank with something basic such as the Sterling Battery Maintainer BM12123 (about $100).  Thanks.  - David

Answer:

Since it's quite common for house battery to get accidently discharged so low that you could not start an engine, we strongly suggest your keep your house and engine battery separate.