2 batteries?

[Xavier]

I am curious as to what is the rule, if there is one, on when to utilize two batteries within your car for more cranking power? I have seen both small and large blocks with them, small compression ratios with no more devices than a full pump and 2 fans. Technically speaking (not for bragging rights) when and why would it be required and what other motifications would have to be done, if any, to use them?

[1985 CCX]

I think two batteries are required when you place them correctly behind the passenger seat. It is my understanding they are usually two 6 volt batteries connected in tandem?

Those that have installed batteries behind the passenger seat please clue us in. I plan to S/C-ize my battery set up this winter and could use the information as well.

John, Double Ugly, what was your set up like? You were kind enough to send pics however details I have lost.


Thanks again!

[Xavier]

Yeah, thanks but I was referring to 12v systems. For a 6v I can understand. But on a small block low compression vehicle is it just for bragging? Wouldn't the 2 batteries be based on how many electrical goodies you have to power and/or the high compression ratio of the engine (regardless of block size) and the difficulty it would have starting? Assuming it exceeds the CCA needed from one battery?

[ENTDOC]

you should never need two . Some cars,
csx and Kirkham for instance often use 2 small 12v batteries( still 12v total) behind the seat, it is a size issue not cranking power issue

[jdog]

2ea 6v batteries behind the passanger seat. Just like back in the day!



jdog
P.S. The 2ea 6v batteries wired together have more cranking amps that a 12v alone. But they really used the 6v's because they couldn't fit a 12v behind the seat!

[shelby racer]

Originally Posted by Xavier

Yeah, thanks but I was referring to 12v systems. For a 6v I can understand. But on a small block low compression vehicle is it just for bragging? Wouldn't the 2 batteries be based on how many electrical goodies you have to power and/or the high compression ratio of the engine (regardless of block size) and the difficulty it would have starting? Assuming it exceeds the CCA needed from one battery?

Due to the size constraints of putting them behind the seats they used two 6v batteries wired in series (?) - I always get series vs paralell confused - so you have about the same number of cca but 12v instead of 6v. Two 12v batteries wored in paralell (?) - like my old diesel truck - doubles (assuming the batteries are equal) the cca.

[computerworks]

Originally Posted by shelby racer

I always get series vs paralell confused -

Batteries in series add up the voltage, but the current stays the same as one.
Batteries in parallel add up the current, but the voltage stays the same as one.

[xlr8or]

I have 2 ea. 12V behind my seat. They are small, group51 I believe so they are only about 300 cca each.

[rokndad]

Mine are two Gill G-35's dolled up to mimic Rebat Executive R-35's. 2-12v batteries in parallel yield only 500 cca's. But it really looks close to what were in some of the 60's cars. The new caps totally seal up so I don't fret about electrolyte leaking any more. And they have the little check balls in them to prevent spills when inverted!!! A little pricey though at about $150 per. See my gallery. I haven't learned the "put the picture in the text" game yet.

[1985 CCX]

Great info guys!

So is in parallel - to - and + to +?
Would tandem be - to + - to +?
I was thinking about adding the two 6V from Optima but the Rebats are great.

For rokndad: What are the actual batteries-brand and type#) you use?

[rokndad]

Jeff,

You have to tell me how you got that picture from my gallery to within the message!! PM or do it here, but let me know.

I have another thread I just posted this weekend on the details of where to get the batteries with free shippping. Look up "Recreating Rebat Batteries" and you'll see the pictures and the links to Gill Batteries. They are Gill G-35's.


Recreating Rebat R35 Executive

Thanks,

Tom Remillard

[rokndad]

Yes, the answer is - to - and + to + is in parallel. The voltage stays the same (12v) but the cranking amps are added (250 + 250 = 500 cranking amps). Each Gill G-35 only has 250 CCA's which even when added is marginal for a high compression 427. But they seem to turn mine over pretty well. We'll see after a while. The manufacturer recommends putting it on a battery tender when not in use. I'll have to get one.

[double ugly]

Originally Posted by 1985 CCX

I think two batteries are required when you place them correctly behind the passenger seat. It is my understanding they are usually two 6 volt batteries connected in tandem?

Those that have installed batteries behind the passenger seat please clue us in. I plan to S/C-ize my battery set up this winter and could use the information as well.

John, Double Ugly, what was your set up like? You were kind enough to send pics however details I have lost.


Thanks again!

Sorry about the delay. I just got back from the Reno Air races. A friend had a Formula One Racer entered. He did well. A rookie and finished 13th out of twenty four.
It's an originality thing. Costs more but yes two six volt hooked in series. Never needed a battery maintainer. The carbon car has two dry cells hooked in series. The cost is about the same but lighter and smaller. I'll attach pics when I get over to the shop.
John

[Sal Gerace]

Very important! When using a battery tender you must charge each battery seperatly(dis connect them from each other). I learned this the hard way after having a boil over from one of my batteries. I caller the battery tender people and they explained to me that I must charge the batteries seperatly because of the way the battery tender reads the battery.

[CHANMADD]

Why would you want battery acid in the passenger compartment?

[Sal Gerace]

Not many want the acid in the compartment,but... The aircraft batteries have taller caps with a check ball in them so you should not have any laekage. But if you do like I did and have always done which is charge my betteries with the caps loose. Like I explained above this could boil over the battery. With these caps I would just leave then tight.
Gil alsosells a Gil35S which is the sealed version of the rebat size battery, but the caps are not as tall unlike original rebats.

[jdog]

Wow, no wonder my 427fe fires right up with barely a touch of the key! Each 6v Optima has 800 cca!

800 cca + 800 cca = 1600 cca!!! = VAROOM!

My car barely turns over once and it starts!

jdog

[Sal Gerace]

I ditched the Shelby supplied cables and went with #2 welding cable. With the long positive to the solnoid I did not want any problems. I did a some research and it seems like this is the way to go.

[sharpe 1]

I owned several British cars during the 60s.They all used (2) 6 volt batteries in series to get 12 volts. They were usually located under a tray behind the seats.Most in those days were positive ground.I think it was a space issue.

[kris-kincaid]

Jdog, two batteries wired in series have the same amp-hour capacity as one individual battery, but double the voltage. Only when you wire batteries in parallel do you obtain multiples of the amp-hour capacity, but wiring batteries in parallel does not increase battery voltage.