Bridgkick wrote: Fri Apr 11, 2025 5:41 pm
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.