Battery charging or trickle charging two batteries

[Marken]

Sorry if this has been asked before. I did try searching the forum first. What is the proper way to connect a charger to a two battery 1970 911T? Do you just connect to one of the positive terminals and one to ground? Thanks very much!

[Joe Bob]

Pull them out and charge on the bench. Once charged a trickle charger will maintain them, assuming they are in good shape.

[Marken]

Originally Posted by Joe Bob

Pull them out and charge on the bench. Once charged a trickle charger will maintain them, assuming they are in good shape.

Thanks. Once charged and put back can I use one tender hooked to one of the batteries?

[timmy2]

Yes.

[wwest]

Are we talking two 6 volt batteries in series or two 12 volt batteries in parallel? Previous would be my guess based on vintage.

[Bob Kontak]

Originally Posted by wwest

Are we talking two 6 volt batteries in series or two 12 volt batteries in parallel? Previous would be my guess based on vintage.

Little battery compartments in the inner fenders. One on each side. 6V each. A pal has a 70T so I seen them with my own two eyes.

[Marken]

Originally Posted by wwest

Are we talking two 6 volt batteries in series or two 12 volt batteries in parallel? Previous would be my guess based on vintage.

Yes. There are two batteries. One in each side of fender. The batteries are marked Interstate U911-50. I didn't see voltage. Possibly as you say 6v wired in parallel. Would hooking up trickle charger on one take care of both? Thanks!

[dafischer]

They are both 12 volt. And hooking up the trickle charger (Battery Tender?) to one will keep both at the proper charge level.

[Bob Kontak]

Originally Posted by Marken

I didn't see voltage. Possibly as you say 6v wired in parallel.

NO - 6 volt X 2 wired in series as wwest says. Doubles the voltage.

6 volt in parallel would give 6V but be a long lasting battery vs a single one.

Connecting Batteries in Series or Parallel

However, it could be either, depending on how wired. Believe original was 6V in series.

[Joe Bob]

Should be 2, 12v batteries on each side for weight and balance.....early short wheel based rides also had lead ballast up front if I recall.

Alternators are not designed to charge batteries but to maintain charged batteries. 110v chargers should be used to bring a good battery to 12.8v+....trickle chargers should be used to maintain batteries in rides that sit more than 2 days or more.

Just my experience.

[964TargaC2]

6v battery has three filler caps not six

[wwest]

Originally Posted by dafischer

They are both 12 volt. And hooking up the trickle charger (Battery Tender?) to one will keep both at the proper charge level.

Very few John Q Publics (some do) would make the mistake of hooking 2 lead-acid batteries in parallel, let alone Porsche design engineers.

[wwest]

Originally Posted by Joe Bob

Should be 2, 12v batteries on each side for weight and balance.....early short wheel based rides also had lead ballast up front if I recall.

Alternators are not designed to charge batteries but to maintain charged batteries. 110v chargers should be used to bring a good battery to 12.8v+....trickle chargers should be used to maintain batteries in rides that sit more than 2 days or more.

Just my experience.

Knowledge often trumps experience.

Connect 2 lead acid batteries in parallel = asking for an .....

EXPLOSION

Cell shorts, goes flat, in battery "A", battery "B" begins dumping FULL CHARGE into battery "A", Electrolyte in battery "A" begins to boil...OUTGASSING...small spark...

BANG!


Plus it is a practical impossibility to fully charge 2 lead acid batteries connected in parallel.

[wwest]

Originally Posted by Joe Bob

Should be 2, 12v batteries on each side for weight and balance.....early short wheel based rides also had lead ballast up front if I recall.

Alternators are not designed to charge batteries but to maintain charged batteries. 110v chargers should be used to bring a good battery to 12.8v+....trickle chargers should be used to maintain batteries in rides that sit more than 2 days or more.

Just my experience.

"...Alternators are not designed..."

In my ~55 years of driving I have jumped, or had jumped, LOTS of otherwise DEAD car (tractor) batteries. I was NEVER advised, and have NEVER advised anyone, to use anything but the automotive electrical system to bring the jumped battery back up to standard charge level.

Automotive battery charging systems, voltage regulators, are designed specifically for recharging a dead lead acid battery at a controlled rate, raising the target charge voltage as the battery charge level rises so as to not overheat the battery during recharge.

[timmy2]

Interesting thing about having the factory prints to reference is they show the 2 positive posts tied together and the 2 negative posts tied to the chassis.
Parallel connection, so a trickle charger on one battery will charge them both. (Eventually)
Print number SL35 for those that are interested....

[T77911S]

using the car alt just puts a strain on it. everyone at one point in their life has jumped a dead battery then driven the car. it is better to use a battery charger. that way you KNOW the battery is fully charged.

you better talk to FORD. my daughters F250 has 2 batts in parallel.
batteries can "run away" or start self charging. put a meter on one. you will see the voltage much higher than 12v. i have to deal with a LOT if UPS at work. one has 40 batteries that puts out 480v and 40Kva. you will see the batterieis swell. when they have done that, they have probably self charged. i saw one at 18v one time.

[gamin]

My 70 came from the factory with 2 12v batteries in parallel. The U911-50 battery is a 12v made by interstate and fits the battery boxes. May not be necessary but I use a separate trickle charger for each battery.

[wwest]

Originally Posted by T77911S

using the car alt just puts a strain on it.

Very few alternators, or even the old automotive generators, could be considered "strained" when putting out their rated current maximum. Other than inherently poor designs out the factory door. Not that recharging a completely DEAD battery would ever require such.

everyone at one point in their life has jumped a dead battery then driven the car. it is better to use a battery charger. that way you KNOW the battery is fully charged.

Yes, at least for that ONE time...

you better talk to FORD. my daughters F250 has 2 batts in parallel.

So does our Ford MH, but the batteries are only "paralleled" when the starter is engaged?

batteries can "run away" or start self charging.

No, charging circuits might well "run away", and do, but I don't know of any instance wherein the battery itself "ran away".

put a meter on one. you will see the voltage much higher than 12v.

During the charging period the normal fully charged terminal voltage of 13.50 volts (6 X 2.25) might well rise above that level

i have to deal with a LOT if UPS at work. one has 40 batteries that puts out 480v and 40Kva. you will see the batterieis swell. when they have done that, they have probably self charged. i saw one at 18v one time.

Fully sealed batteries, such as are almost always found in an indoor UPS, often fail due to FAILURE of their charging circuits. The SWELLING is due to the extra HEAT causing an expansion of the electrolyte, sometimes even to the point of boiling.

Like electrolytic capacitors, these will generally have some sort of one-time pressure relief valve.

A completely discharged lead-acid battery will initially present an extremely high internal resistance oftentimes resulting on a an unusually high terminal voltage to bring the battery back up to the level required to begin accepting a charge. I have seen it take up to 2 days to complete the cycle.

[Bob Kontak]

Originally Posted by Bob Kontak

Little battery compartments in the inner fenders. One on each side. 6V each. A pal has a 70T so I seen them with my own two eyes.

I did seen them - but my pal told me they were 6V and he does not work on cars.

Unless by a miracle me and my pal Larry are the only ones that know the real truth, and these other guys, like gamin who owns a 70 are clueless, I would defer to the 12 volt in parallel.

12 V in series would be 24V.

Did any of the 356's have 6v systems or 2 X 6 in series?

[dicklague]

Originally Posted by wwest

Knowledge often trumps experience.

Connect 2 lead acid batteries in parallel = asking for an .....

EXPLOSION

Cell shorts, goes flat, in battery "A", battery "B" begins dumping FULL CHARGE into battery "A", Electrolyte in battery "A" begins to boil...OUTGASSING...small spark...

BANG!


Plus it is a practical impossibility to fully charge 2 lead acid batteries connected in parallel.

so why did it ship from the factory that way??