Cable size for connecting main and auxiliary batteries

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Originally Posted by drivesafe

Hi Toxic, the CCA of a battery is the most standardised way to rate a battery's cranking capacity and is the most accurate.

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Without wanting to be a smartarse, and entirely for my own information, what's accurate about a batteries performance at -18C when very few, if any vehicles would be needed to start at this temp? I understand most batteries are sold using this rating, but really seems like selling oneself short of the additional cranking capacity.

Wouldn't most be interested in what sort of amperage the battery can maintain at 'normal' temperatures?
As an aside, in the sciences, we talk about standard temperature and pressure- 1 atmosphere (1 Bar), 25 degrees Celsius, as this is where most reactions would be observed.

Hi again Toxic and I don't think you are trying to be a smartarse at all. That is a logical assumption.

But from all the info I have read about establishing battery ratings, while there are quite a few different rating test formulas used, most are open to different interpretations or can be "fudged" to some degree.

Where as CCA testing requirements are the toughest way to establish the CA of a battery and, in my opinion, give the most accurate rating of a battery's true cranking amps.

Thanks for the information. I'm still figuring out this electrickery, so am taking it slow and steady. I just want to get it right the first time for a long-term arrangement.

There are a lot of different Optima Yellowtops on their website, so I've been trying to work out which one is best for my needs. If I go Optima, I'm going to go with an Optima 31T, I think. I get the impression from the website that the 31T is more for deep cycle uses while the 31A is more dual purpose (but I could be wrong).
Just gotta put aside the cost of the battery, cabling and plugs. Money is a bit tight this month because of other bills.
Incidentally, I know an Optima can be laid on its side because its fully sealed, but is that true of other AGMs? Don't some AGMs still vent if they overheat?
It's not a problem for it to go upright in the camper, so I went for the bigger AGM, but I do need to lay the one in the Defender on its side to make it fit better in the compartment behind the drawer.


I also looked at this battery: http://www.aussiebatteries.com.au/ba...rminal-battery
It seems to have all the right things going for it. What do you think?

I am right in thinking that if my Traxide unit connects the two batteries with the right cables and circuit breakers then, when winching, the winch will be able to draw on both batteries if necessary, aren't I?


Sorry to ask a lot of questions...

Hi Mick and while that battery sounds good, the technical info leaves much to be desired.

It states an unlimited charged current at 13.5v to 13.8v, but has a 30 amp limit on the charge current for voltages from 14.4v to 15v. This could be a problem when used in a vehicle with 14+v operating voltages and a high current alternator, especially if the battery is low when you start your drive.

Also, the cycles at 50% SoC ( same as 50% DoD ) are not as good a Fullriver battery's cycle rates at 20% SoC ( 80% DoD ).

IMO, it's cheap, but for a reason. Also IMO, it's not a genuine AUTOMOTIVE grade battery.

Thanks for that advice, I really appreciate you taking the time out from your work to look at it. They advertise on this site, so I was curious. So, to summarise, at $299 it was a good price, but I guess for $399 the Optima would be better quality.
Incidentally, my Defender's alternator seems to making a consistent 14v while ever the engine is running, from the gauge I have plugged into the cigarette lighter. So, from your comment about the specs, I assume that Giant battery would be limited to 30amp charging while my vehicle was making 14v. I think I've got that right?

Hi Mick and based on the specs they have on their web site, you would need to have some form of current regulation.

And this would completely defeat the CHEAP battery premise.

These batteries sound like they might be good for stand alone systems, but because of the additional cost of some form of current limiting device, they would not be my choice in a vehicle situation.