Dual batteries or single larger battery?

[sifan]

My Odyssey PC1200 (relocated to the trunk) does not provide enough CCA during this cold winter in 10-20F. I am thinking of upgrading it with a PC1700, but do not want to leave the current battery in the basement since it is only about 3 years old out of 8 years of service life according to the vendor.

So, if I bought another PC1200 and set them up in dual battery configuration, then I could put the current battery in use, and also pay less for the second battery. On eBay a PC1700 is sold for $275 including S/H compared with a PC1200 for $175. However, in this case, the two PC1200s would not be of the same age. Will this cause a problem in dual battery setup? Moreover, the two batteries would not sit side by side, but reside behind the rear wheel wells separately. Will this separation cause another problem?

Or just buy a PC1700 and save the headache?

 

[rpn453]

A $175 battery that is inadequate for use in warm weather?

 

[sifan]

The $175 battery served me very well even after I installed a pre-luber kit on my car. In above freezing temp it works fine, but not below freezing. Apparently my current battery (550 CCA) was weakened by the 10-20F temp and further by the pre-luber pump motor, which pushed the extra cold thick oil for 40 seconds during each engine startup.

 

[Gary Allan]

One battery will take most of the insult and the other will provide the difference. It's not as simple as just joining two batteries electrically with cables. Most here, aside from some of the diesel guys, haven't truly used a dual battery setup. They hooked up auxiliary batteries that are typically isolated from each other.

This isn't as much of a downside as one may think. The last thing you need is both batteries reaching the end of their life cycle at the same time. Especially @ $175 each.

The hard part is figuring when one is on the way out.

 

[sifan]

How about charging? Will both batteries get fully charged by the alternator? How many amps are needed to start up a 4-cylinder engine?

 

[Chris142]

Sounds like you need larger cables and not a larger battery.

 

[sifan]

Please skip the cable size issue, which has been discussed to death in another thread. I am more interested in knowing more about dual battery setup. Thanks.

 

[sifan]

The Odyssey PC1200 can deliver 1200A in the first 5 seconds on paper. I usually let the 10A pre-luber pump run for 20 seconds, and then start up the engine while the pump keeps running for another 20 seconds as programmed. I do not know how much juice left in the battery after the first 20 seconds of pumping, and it doest not help the starter while the pump is still operating in order to keep up the oil pressure. Adding the frigid temp that reduces the battery capacity even more surely does not help, either. Yes, it is a $175 battery and is more than adequate to start an engine, but its unique design/behavior might not up to the job in my case.

 

[Ugly3]

If I paid $175 for a battery the SOB better start the engine at -40F.

 

[onion]

WHY do the batteries cost $175 each? If you've relocated the battery, then can't you pretty much put anything you want in there? My cars start great on 5+ year old $40 wal-mart batteries at -10 F. No prelubers here (seems like and AWFUL lot of trouble).

About the dual battery idea... I've worked on trucks and heavy equipment for a dozen or so years, and the vast majority of them have the batteries wired in parallel. Just hook + to + and - to -, then hook up your cables to the front of the car... nothing more complicated than that. I've seen mismatched batteries run many a time- it's not an issue. You'll be fine with two matching batteries, and the age difference won't affect anything.

 

[onion]

One clarification- mismatched batteries can cause problems if they're hooked up in SERIES. I've fought that more than once on 24 volt systems. However, I've never seen mismatched batteries cause a charging problem when they're hooked up in parallel. Unless you plan on running two six volt tractor batteries... you'll be wiring in parallel.

 

[alreadygone]

Chris142,

Please don't bring up something so confusing as facts!

Bob

 

[tom slick]

you'd probably want to install a battery isolator if you install 2 batteries.

it is strange that your battery can't keep up with your load.

 

[Chris142]

Fine. Let em put the cart before the horse.

FWIW two 750CCA batteries will start my 855 cu inch Cummins @20F. Infact it takes alot of cranking to do so and they willl crank it a good 30-45 seconds untill it starts.

Anyway I'll step out now. As ya'll were.

 

[Shannow]

Given the situation, I don't see how two batteries will help much. It's still 12 volts trying to drive the amps down the hosepipe. Doesn't really matter how many amps the battery is capable of supplying if the volts can't deliver it.

Lots of dual battery set-ups in 4WDs down under. Most of the ones that I've seen end up with one empty tray and the terminal clamps taped over when the guys stop playing hard core 4 wheelers.

Remember with two in parallel, if one goes down, the other does too. For that reason, some systems have isolating solenoids between the batteries, others have diodes (meaning one or both batteries never charge properly.

Most guys who relocate their batteries down here use welding leads to connect them up to where the load is used.

Get a bigger hosepipe

 

[Gary Allan]

Quote:

---

I've seen mismatched batteries run many a time- it's not an issue. You'll be fine with two matching batteries, and the age difference won't affect anything.

---

Correct. He'll perceive no issue. But that won't alter the fact that one battery will do the lion's share of the work and the other will take up the slack. That's what occurs in many systems ..especially home grown ones where some "just slap them together in parallel and you'll be fine".

 

[Sparkman]

Dual and/or larger battery seems to me to be a bandaid for another problem. If you haven't done it I would start by characterizing the voltages and currents (and therefore resistances) in the system as a whole and then systematically determine where the money is best spent. My intuition says cables.

 

[brianl703]

You can use a multimeter to measure voltage drop across a section of cable while cranking the engine, which might be more useful than checking the resistance of the cable directly. You might want to put one multimeter lead on the battery + terminal and the other at the starter + terminal, then crank the engine.

Do the same between the battery - terminal and the starter's ground connection.

 

[sifan]

Chris142 - My apology. After reading your experience of engine startup in 20F I think my battery is actually fine.

In 20F as I turned and held the ignition, my engine would turn over 3-4 times very slowly (feel like there wan not enough battery power), and then fired up right away under 5 seconds. I guess I was spoiled by all the engine/fluid heating devices, and became overly paranoid when the engine did not start up like 4th of July as ugly3 put it even in cold temp. Now I can see my engine/fluid heating devices are indeed very useful and effective. I have been carrying the portable generator in the trunk, and fired it up for one hour to drive the engine/fluid heating device plus charging the batter for the last several weeks. Even in a 10sF evening my engine fired up right away.

So far, my battery has never failed to start my engine. I will keep it the way it is, and see no need for battery upgrade. Thanks all for your inputs.

 

[sifan]

The following is the reply I got from an Odyssey battery dealer:

"Absolutly, any of the odyssey batteries from the 545 and up will start a car. The pc1200 has more then enough umph to start a car engine. My business partner has a pc925t in a t bucket with a 350 ho and it spins it over really good. The "t" stand for automotive type terminals. We have them in stock if you need them for $9. Call us directly if you need a set. Our number is 626-358-0763. We are here from 7-5 (pst),mon-fri. Thanks for the inquiry."