Battery options for EOC - long distance

[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?

[VegasDude]

I think with a new battery you'll have less of a problem. The same thing was happening to me with a 5 year old battery, then again with a one year old battery, but I also think the Vegas heat was taking it's toll as well.

If you have a manual, another option is to install an engine kill switch. I've done the same thing, and when approaching a light I know is going to be red by the time I get to it, I can force the engine into DFCO even if the revs are too low to normally allow it. I'm not using any extra gas to do this, since I would normally use EOC and the brakes. The extra time that the car is in DFCO helps keep the battery voltage up. I also have a digital voltage readout in the car and if I'm running low, I'll bump-start the car before I stop at a red light. Otherwise I run the risk of having to get out and push.

If you were to buy a new battery, place it anywhere in the car, and wire it in parallel with the old battery, you WILL need a heavy duty cable if you plan on starting the car without disconnecting it first. There's no way to tell which battery to supply the current if they are both connected at that time.

I've also thought about using a seperate lipo battery for the head lights, or building custom LED bulbs with a few 5 watt LEDs in place of one 55 watt halogen.

[RobertSmalls]

If both batteries are at the same voltage all the time, you'll end up deep cycling them both. Can you find room in the engine bay for a marine dual purpose battery?

There's also the junkyard battery option. Buy fresh 51-series batteries for $15 each, and abuse them. You'd have to get at least a year out of each battery for this option to be economical.

VegasDude gave me an idea which seems to be worth thinking about. Run your starter off of one battery, and attach the power distribution box + the alternator to the marine battery in the trunk. You can get away with narrower cable that way. You can grid charge both batteries when you get home. I hope you don't do too many key starts.

[brucepick]

Thanks VegasDude.

Yeah I think you're right about the heavy cable. I just did some reading on the "big three" upgrade, and that article said the same.

Car is manual trans.
Has a kill switch but it only cuts power to the fuel injectors.
Also has a digital voltage readout.

[VegasDude]

Originally Posted by brucepick

Thanks VegasDude.

Yeah I think you're right about the heavy cable. I just did some reading on the "big three" upgrade, and that article said the same.

Car is manual trans.
Has a kill switch but it only cuts power to the fuel injectors.
Also has a digital voltage readout.

Exactly how mine works. Flip the switch in gear to start DFCO, since the motor is still turning, torque is being delivered to all accessories.

[dcb]

I have the deep cycle battery from wally world in my saturn, was like $60 and took a little "finesse" to get it to fit. It is manageable, but the voltmeter (or some other state of charge indication) is a great idea so you know when it is time to spin the alternator.

I had one in my metro too and disabled the DRLs and put low consumption LEDs on the corners, never, ever had a problem there.

But I can also bump start all of these cars, by hand if it comes to it, so with a stick shift and a smallish car I don't lose much sleep over it.

The other genuine plus of the deep cycle is longevity. I have run them down completely dead several times (sometimes EOC coast into the garage and forget to turn the car off) and they are still in service, though one needed water recently. The typical starter battery never lets me get away with that.

[euromodder]

How about batteries for diesel cars ?
They have a lot more Amps and Oomph !
With 2 of them mounted in parallel, I doubt you'd drain them in an hour.

[brucepick]

Originally Posted by VegasDude

Exactly how mine works. Flip the switch in gear to start DFCO, since the motor is still turning, torque is being delivered to all accessories.

Ouch. I'm going off topic here, but - - -
In my experience, the loss of momentum from keeping the engine in gear far, FAR outweighs the small gain you receive by keeping the accessories going. That is, assuming a standard transmission and also assuming you're not trying to control a case of runaway steep downhill coasting speed buildup.

If ya wanna cut fuel and gain the most from it, put it in neutral ASAP, kill the engine and let her roll until the speed drops to the lowest you or the law or the traffic will accept.

[brucepick]

Originally Posted by dcb

I have the deep cycle battery from wally world in my saturn, was like $60 and took a little "finesse" to get it to fit. ... the voltmeter (or some other state of charge indication) is a great idea so you know when it is time to spin the alternator...

Good idea, I'm going to look into that. I do have a dig. voltmeter on the ScanGauge, which is I keep an eye on regularly now. I tried to find a marine battery in my Civic's size (51R) but no go. But shucks, maybe I can "make it fit". Wouldn't be the first time I did that!

[RobertSmalls]

The SG's voltage readout isn't accurate, but it is consistent. Mine's always ~1.0V lower than the voltage at the battery, and IIRC another EcoModder reported a ~0.7V drop.