992 Turbo Dead Battery Charging

[gthal]

This is very helpful. Thanks!

[Bridgkick]

I'm working to open up my 997.1 with a dead battery. These instructions are similar to other articles I've read.. but my brand new Noco GBX45 1250A gives a short-circuit error even when I put it in manual override mode. Has a anyone run into this? Is it just underpowered?

[Tom]

I'm working to open up my 997.1 with a dead battery. These instructions are similar to other articles I've read.. but my brand new Noco GBX45 1250A gives a short-circuit error even when I put it in manual override mode. Has a anyone run into this? Is it just underpowered?

I highly doubt it. I could not get any of my 'smart' chargers to work -- even when I set them to not look for a battery. I ended up using a 1970's battery charger from Sears that just supplied 12 volts without trying to be smart. Most porsche manuals show an actual car battery as the source for powering the frunk jumper. If need be, you can use jumper cables from another car, though you might need to fashion smaller clips to get them on there. Good luck!

[dr bob]

I'm working to open up my 997.1 with a dead battery. These instructions are similar to other articles I've read.. but my brand new Noco GBX45 1250A gives a short-circuit error even when I put it in manual override mode. Has a anyone run into this? Is it just underpowered?

Kind of off-topic with 997 in 992 turbo discussion, so this is really sort of a tangent.

Unless your 997.1 has a lithium battery with the built-in BMS (battery management system), it's got a normal flooded-cell lead-acid battery or AGM (absorbed glass mat). The BMS in the lithium battery protects the cells from depleting completely, while a FLA or AGM battery will in fact run itself completely dead.

Your lithium jump-starter box protects itself the same way with its own BMS system. It looks for correct polarity, so you don't cross the terminal clamps and fight the battery in the car rather than boost it. To do that, the cells in the booster pack would be instantly pulled to zero volts or less, ruining them. If the booster can't detect any voltage at all, it can't really tell if it's connected correctly unless/until it sends a small test voltage. A completely dead AGM or FLA battery will have a very low internal resistance, so won't respond. The booster then assumes (correctly) that the load is too great for it to "boost".

We buy "1500A" boosters that will never actually deliver 1500 Amps for more than a few milliseconds on their best days. A small bank of lithium cells charges a capacitor in the booster box, supplementing the current available from the car battery to get it started. One I have offers a bit of 'surface' charging to the car battery prior to supporting cranking, but the net effect is still the same. It doesn't supply enough current from those tiny cells to both charge a completely dead car battery plus support a few hundred instant cranking amps. "Smart" chargers use some of the same logic, forcing us full-depleters to use dumb chargers to restore at least some of the basic charge before we use a smart charger maintainer to finish the job.

I could write a long treatise on car batteries and how they suffer when over-discharged. I'll summarize it into a recommendation that you just replace the battery you drew to stone-cold dead. It will probably appear to charge OK, but will never be as reliable as you want it to be. It will present extra load on your alternator for the rest of its now-shorter remaining life. Last I looked, batteries were cheaper than alternators, and way cheaper than a flatbed. Of course you do have your jump-start box to perhaps avoid the flatbed, assuming the flatbed was for a dead battery and not the failed alternator. Have it tested after you get it charged again, and use that to help drive your replacement decision of course.

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My relatively ancient car has the battery disconnected during hibernation season now, so the 'normal' parasitic drain current doesn't cause the battery to 'cycle' on the connected maintainer. The battery ground strap snakes up out of the battery well under the spare wheel in the boot to a connection point on a rear frame member. Just lift that connection and the battery is isolated from the rest of the car. I fashioned a little fused charging harness that's bundled with the ground strap, and has a connector right by the frame end of the ground strap for charging/maintaining whether the strap is connected at the frame or not. The space for the ground strap connection is pretty tight, as designers worked to stuff things in virtually every tiny space the could use. In the last few weeks I've found what I think may be the right battery-disconnect switch solution to fit there, but need to get the car down off storage stands and into the workbay for the actual fit-up. Film at 11 in the 928 forum when it's done.

In the meanwhile, there are many battery disconnect options for cars that aren't quite so space-cramped. Some casual shopping will offer some options, from relatively standard twist-lock isolators to simple screw-knob versions, and some that clamp directly to the battery post and accept the existing cable clamp. There are some interesting little radio-remote isolators that may or may not be useful for storage situations. For me, the KISS method with a manual switch will do fine, if I can get it to fit in the cramped quarters behind to toolkit panel.

TL;DR --
There are plenty of supposedly-capable maintainers on the market. For a long time I used a pretty simple 1.5A Schumacher version, and left it connected while I was away on business for more than a few days. Than an accidental full-depletion event happened when we were moving. I drove the car to the new home where it sat for a month before we officially relocated, and had accidentally not completely closed the glovebox door after grabbing DMV paperwork.
Like Tom, I had to resort to a stone-age charger to bring the battery back closer to alive, but the 1.5A 'smart' maintainer still took a few days to bring the battery back to fully-charged condition. That one was quickly retired to loan-out service, and replaced with CTEK US7002 maintainers for all the cars. Porsche and Mercedes both rebrand these for their own customers, and for a while they shipped with the cars to dealers (who harvested and resold them...). I've since received several different smart maintainers for test/evaluation, all costing a lot less and cheaper too. The price on the 7 Amp CTEK has more than doubled in the ten years or so since purchase, now close to the cost of a new battery. I might consider the 4.3A version were I buying today, but probably nothing less at least for the cars we have now. They do have lithium battery capability, plus a 'restore' function that was able to extend the life of that discharged-to-flat 928 battery to over a dozen years.

Battery 'care' here includes at least annual capacity evaluation, using a simple specific-gravity tester. Batteries that don't pass at full capacity get replaced, as simple as that. Doesn't work for lithium or AGM batteries obviously, but for conventional FLA batteries it's a practical alternative to getting stranded and/or demolishing an alternator trying to maintain charge on a battery that won't take it anymore.

[cassius]

I have a 991.1 (2012) Carrera. My garage locks securely when we’re traveling, so what I do is pop my hood latch and leave it ajar for the duration of travel. When we return, I trickle charge the battery to full. I have not had a full depletion, so this might not work at all in that case.

If anyone knows why this might be a Bad Idea, I’d appreciate feedback!

Great discussion and good lessons documented here.

[Hawkestone]

As an owner of a 2020 992 and a 2019 991.1 Speedster, I have had dead batteries in both. The 992 was rescued by the instructions laid out previously… I call it ‘shock and awe’ and it works well with the lithium ion battery of the 992.
However my Speedster’s battery was completely dead upon my return to Arizona (yes, it was on an appropriate trickle charger), I tried the aforementioned fuse box trick with the ‘shock and awe’ but the frunk would not open no matter how I shocked it.
And then the AAA Technican who came with his flatbed tried pushing the frunk opener on the key fob while shocking the fuse box pullout, and wow the frunk opened! I was amazed.
I also learned that here is a manual frunk opener on most modern 911s, in the driver’s side wheel well. However you must remove the wheel and some plastic moulding to get access to this manual pull.
I now consider myself an expert in modern 911 dead battery rescues.

[Tom]

As an owner of a 2020 992 and a 2019 991.1 Speedster, I have had dead batteries in both. The 992 was rescued by the instructions laid out previously… I call it ‘shock and awe’ and it works well with the lithium ion battery of the 992.
However my Speedster’s battery was completely dead upon my return to Arizona (yes, it was on an appropriate trickle charger), I tried the aforementioned fuse box trick with the ‘shock and awe’ but the frunk would not open no matter how I shocked it.
And then the AAA Technican who came with his flatbed tried pushing the frunk opener on the key fob while shocking the fuse box pullout, and wow the frunk opened! I was amazed.
I also learned that here is a manual frunk opener on most modern 911s, in the driver’s side wheel well. However you must remove the wheel and some plastic moulding to get access to this manual pull.
I now consider myself an expert in modern 911 dead battery rescues.

As far as I understand it, the fuse box terminal is used solely to supply power directly to the trunk-opening solenoid so that you can pop the frunk and get to the battery (i.e., it doesn't charge the battery itself at all). Once the solenoid is powered, I needed to push the button to open the trunk. On some (most? all?) cars, only the key fob works to pop the frunk though -- since the solenoid and its receiver are the only things with power -- so that may explain why it didn't open for you but did for the AAA guy...

[dr bob]

A similar-project update. A neighbor's E55 has the battery in the trunk, and of course an electric-only release for that. There's access to a cable terminal in the passenger's footwell after removing a bit of mat, carpet, padding, sound deadening, a mounting plate and heat sink for control modules, a thin composite panel, then finally I can get to the cable connection. Part of the process here will include a new battery, and I'll almost undoubtedly add a fused pigtail and connect it to that cable connection, route it out around all those intermediate layers to a safe spot above the passenger's feet. Then I can attach her maintainer while the car hibernates for winter, and be able to charge the battery enough to open the trunk should that need arise.

On the Porsche models in question, think about where there's a decent 30 bus location in the passenger compartment. Might be as easy as a header rail in a fuse and relay panel, or even a power seat motor supply cable where you could add an intermediate connector piece (printed?) to safely and cleanly (no factory wiring hacks) push some power back towards a deleted battery in a pinch.