[brucepick]

I've been working the EOC technique pretty hard with good results. However my commute is about 55 mi each way and that much EOC runs down the battery. Too much time with lights and everything else running, but alternator is "out to lunch". I've seen more than 35% of my distance being EOC, reading from the MPGuino. And the voltage drops towards 11 and will go lower... The Civic has a small battery, Group 51R, so even when new it holds only so much charge and will get run down. Remember, one hour commute, longer on the small roads that are best for EOC.

I'm considering adding a second battery in the trunk. So - what are my options? Maybe a marine battery back there? I might be able to get a semi-used one from a neighbor... Or a regular automotive starter battery back there? I have a spare I could put in.

In either case I could set up to charge the system overnight from house current so the engine doesn't have to do it while commuting.

Optima yellow top to replace the regular battery would be nice but I can't spend that kind of money (approx $175-ish). The regular battery is over 5 yrs old so I can justify replacing it; I can get a new better grade one (more CA and CCA and more reserve than the cheapo) on sale now so I do hope to do that within the next day or two. But I think it still needs more battery capacity to go the distance.

If I put a marine deep cycle battery in the trunk plus a regular one up front, I figure they would each contribute when their particular strength is needed - the standard one for starting, and the marine just hanging in there during repeated EOC. Or would I be better off with a second automotive starting battery?

Opinions please? Especially if you're an electrical engineer, speak up!!

Oh yes. I don't think I need a super heavy cable for the rear battery because it's really intended to support only the running and EOC loads, not starting. Am I right about that?