It really depends on what batteries you have. The good news is that usually our engines are small and don't require a lot of starting current.
Theoretically, the starting batteries have thinner plates, are able to provide high current (cranking amps) and expect to be used only for a short period and quickly recharged. The house is just the opposite: thick plates, generally lower current, higher level of discharge allowed. Then there are the "universal" ones that are a compromise (not particularly good for either).
If it works for you, you can use a "house"-type battery for starting. If it can provide enough current to start your engine, you are ok. Your system would work particularly well if both batteries are the same kind.
I think that the current thinking is more about prime and spare than about start and house. The idea is to use the house bank (if you sail without access to shore power for long periods, you need a big house bank) for everything and keep a small spare (emergency) battery for starting, if your house is exhausted. Btw. You don't use 1-2-both switch in that configuration; rather, you connect the house bank directly to the "out" of the alternator and charge the spare through an ACR or an Echo Charger.
There is plenty of information on the topic at Maine Sail's web site. Very good read.
Marek Dziedzic
1994 C270 "Legato"
Ottawa
Bev Parslow via CnC-List
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