It's always best to match batteries to the same amphr rating. IE a 240 amphr Trojan 6V golf cart battery circuit should have a similar +/- 20 amphr start battery. I prefer to also keep all the batteries the same brand or at least have the same factory settings for charge/float etc. We just changed out our Trojans for 251 amphr 6V Interstate and a 12V Interstate marine start/house battery. This allows the batteries to absorb equally putting less strain on the charging system.
mitiempo was being nice!
This is just plain WRONG. Let me spell that: W R O N G
There is no earthly reason why start batteries need to have an amperage capacity anywhere near the house battery bank.
Especially not with EchoCharge or DuoCharge technology, or even with some of the other methods of "combining" batteries.
One poster on these Boards has 10, count 'em, 10 4-D batteries aboard, total over 2,000AH capacity. I'm just gonna guess that his start battery isn't anywhere near 2,000AH capacity!