Battery Disconnect

[Rtrorkt]

Have a very small parasitic draw on my electrical system. Something like 2 to 3 milliamps. Shops don't seem to want to find it. Full disclosure, chassis is 69 with 86 motor so a mishmash of various systems

I have a trickle charger but had a complete brain cramp and did not plug it in. Gong to cars and coffee yesterday and it was dead as a door nail. Operator error. Duh

Talking with folks, the comment was a battery disconnect might be better all around. Will not let the battery discharge and I suppose the worst result is the clock is wrong. I have an Odessey battery in it. Maybe something like this.



Or keep the trickle charger and just remember to plug it in?

[walt]

Thats a very small mA loss and it may not be your problem. Load test the battery and clean your ground straps before going any further.

[John W.]

I would not worry about a 3 mA drain. It’s probably the clock. A recent poster had a 15 mA drain and doing the math his battery would last several months. Your battery would last five times that.

[Rtrorkt]

Thanks, did the ground straps cleaning. Have not tested the battery. Been flat 3 or 4 times in the past 8 months or so.

Advice is to keep the trickle or go with the disconnect?

[fanaudical]

Get your battery tested.

I just had to replace the H6/group48 lead acid battery in my 911 after 10 YEARS (Interstate battery from Costco) because it finally wore out. No battery disconnect on mine. It goes on the trickle charger if I haven't driven it for a week.

Installing a disconnect would mean resetting the clock and radio every time I turned the battery back on. Am not sure about your car's battery location, but mine has the positive terminal near the fender. I'm not sure how I would get a battery disconnect switch to fit there...

EDIT: DOH! I could put the disconnect on the ground side where there is room...

[walt]

You need to find and fix the problem. Do you really want to deal with a cut-off every time you park the car.

[Rtrorkt]

its a 69 tub, so I have the Odessey in the left battery box and it is tight for sure. Think I will just keep with the trickle charge and just smack my forehead or something to remind me to plug it in

[Aztim]

That specific cutoff switch doesn't seem to be the best design, I see it damaging the battery terminal over time

But yeah fix your parasitic drain

[MTN930]

Parasitic drains are a real pain in the .... reads like you're doing the right things to try and deal with it. Lots of good advice, it is best to find it.

To your questions about a cutoff switch, they work great and are pretty handy for longer-term storage. Over the years I've had a couple of them in different cars.

The Hella Battery Master Switch (red in the reply) and also the Rennline terminal (orange in the reply - available from our host). Hella had a 100A rating the Rennline a 350A rating. They seemed to work fine (wired them in the negative terminal side of things) w/o any noticeable difference in performance between the two.

Good luck.

[ToySnakePMC]

Just installed this old school Hella near the battery and bolted thru the panel behind the front bumper. The Amazon special I had the previous 5 yrs finally gave up. I just don’t care for any of my old or specialty cars with batteries connected all the time. My buddy turned me on to BatteryCableUSA dot com for some awesome short cables with the ends I neeed. Was not disappointed with this small project.

[A930Rocket]

Use the trickle charger. It’ll maintain the battery and besides, you’ve got to remember to plug it in or turn off the disconnect. Either way, you have to do something.

[911 Rod]

I'd start with the battery. They don't like to be drained. Keep it simple.

[RDM]

If the battery has been flat a number of times recently, it may be time for a new one. As someone stated before, have the battery tested.

I have used my battery charger to recondition (and therefore resurrect) several batteries that gave every evidence of being done, including a deep-cycle AGM battery. Definitely worth having.

CTEK - 40-206 MXS 5.0 Fully Automatic 4.3 amp Battery Charger and Maintainer 12V

[Schulisco]

side note: Once a lead acid car battery was deep discharged it's predamaged for the rest of its life. It may be resurrected of course but it won't reach full capacity and lifetime any more:

https://www.ufinebattery.com/blog/what-is-deep-discharge/

What happens during deep discharge?
When a battery undergoes deep discharge, several critical changes occur:

Voltage Drop: As the battery discharges, its voltage decreases. Each battery type has a specific cut-off voltage where it ceases to function effectively. For example, lead-acid batteries typically should be discharged at 10.5 volts.

Increased Internal Resistance: Deep discharging can increase the battery’s internal resistance. This makes it more challenging to recharge effectively and can lead to overheating during charging.

Potential Damage: If discharged too profoundly, particularly in non-deep-cycle batteries, irreversible damage can occur. This may include sulfation in lead-acid batteries or lithium plating in lithium-ion batteries. Sulfation occurs when lead sulfate crystals form on the battery plates during discharge and do not dissolve into the electrolyte during charging.

So prevent a deep discharge under any circumstances!

Thomas

[famoroso]

I've been wanting a non-invasive battery cut-off switch mounting solution, for use with a Group 48 battery. My thought was a battery hold down that incorporated a switch. I asked for that in the Rennline thread long ago. Never got a response...

Originally Posted by famoroso

Would you guys consider making a combination Group 48 battery hold down bracket / cut-off switch mount?

When using the smaller Group 48 battery (as opposed to the longer Group 49), both M8 bolt mounting points are available in the pan. I was thinking of a hold down / mount that serves two purposes: 1) replaces the factory hold down (911 611 209 00) and B) acts as a mount for a battery cut-off switch.

Thoughts?

Thanks in advance,

[Schulisco]

Originally Posted by famoroso

I've been wanting a non-invasive battery cut-off switch mounting solution, for use with a Group 48 battery. My thought was a battery hold down that incorporated a switch. I asked for that in the Rennline thread long ago. Never got a response...

I have to admit that I don't know a solution for you. But I do not get why people use an AGM battery in vintage cars...IMO completely senseless unless you modify the alternator to increase the voltage. Even then still no benefits due to absence of start stop systems. I doubt that they will last longer or bring other benefits like weight saving.
Any way everybody's own decision...

Thomas

[famoroso]

Originally Posted by Schulisco

I have to admit that I don't know a solution for you. But I do not get why people use an AGM battery in vintage cars...IMO completely senseless unless you modify the alternator to increase the voltage. Even then still no benefits due to absence of start stop systems. I doubt that they will last longer or bring other benefits like weight saving.
Any way everybody's own decision...

Thomas

That was six years ago. This'll probably really bake your noodle, but... I run Li-Ion nowadays. 😎

At 19.5 lbs, this 60 Ah Li-Ion weighs 35.1 lbs less than this "baby's coffin" flooded Group 49 battery at 54.61 lbs

[911 Rod]

Originally Posted by Schulisco

I have to admit that I don't know a solution for you. But I do not get why people use an AGM battery in vintage cars...IMO completely senseless unless you modify the alternator to increase the voltage. Even then still no benefits due to absence of start stop systems. I doubt that they will last longer or bring other benefits like weight saving.
Any way everybody's own decision...

Thomas

Please explain?

I've been using a redtop Optima for years.

[Schulisco]

Porsche used not for nothing bigger (and in the very early days of long nose 911's two of them) heavy lead acid batteries to improve front to rear weight balance. When you take weight from the front to the rear the center of gravity moves more and more in the back where the 911 already has the most heavy part. The handling of the 911 is more or less like driving with a big pendulum. My SC handles way better with tank full of gas. Half emptied and less worsens the handling again.

AGM needs higher voltages to get fully charged (14.7volts IIRC), the original alternator only delivers roughly 14 volts. So the AGM never gets fully charged by the alternator unless you charge it at home with an appropriate charger.

LiOn batteries are not that robust being misused as a car starter battery due to temperatures, current, long sitting times, vibrations etc. for which they have never been intended. On todays electrified car batteries almost every single cell has it's own battery management with temperature and voltage surveillance etc.. Complete different story. Not feasible in a starter battery. I've read many reports of failed optima batteries in the past. Too many for my taste. Most of the Optima users got back to conventional lead acid batteries. The Optima may work on race cars being used only a few days a year in best wheather conditions... But for a vintage aircooled 911 being run from time to time in public traffic IMO it's waste of money and effort. You won't go faster or corner quicker with such a battery and still you gonna loose every "race" against todays hot hatches and sports cars anyway, no matter if they're combustion or electrified cars. Not all things were bad in the old days...the aircooled 911 is the best example.

LMAO - I've never seen those "Anti Gravity Batteries" before - they cost up to 1000bucks and more... For that much money I'll buy 10 old fashioned acid lead battery and will feed my 911 for the next 100 years with starter batteries...if we will have gasoline that long ... LOL
Also they claim by theirself that these batteries are best for racing appplications - self explaining. No further questions. End of story.

Don't get me wrong. No blaming. Anybody is free to make own decisions. Just my 2 cents.

Thomas

[Rtrorkt]

all good information. Thank you all

Think I will keep the trickle charger, using the CTEK. And will probably just get another Odessey. I did put a new alternator in it, need to see the model. The guy that built the clone used the Odessey from the get go so that is where it is wired. And hear you on the weight thing. Not racing just some fast driving, within my limits, from time to time.